15.34% efficiency all-small-molecule organic solar cells with an improved fill factor enabled by a fullerene additive - Hu, Dingqin; Yang, Qianguang; Chen, Haiyan; Wobben, Friso; Le Corre, Vincent Marc; Singh, Ranbir; Liu, Tao; Ma, Ruijie; Tang, Hua; Koster, L Jan Anton; Duan, Tainan; Yan, He; et al. (Energy and Environmental Science, 2020)
Solution processed organic solar cells (OSCs) composed of all small molecules (ASM) are promising for production on an industrial scale owing to the properties of small molecules, such as well-defined chemical structures, high purity of materials, and outstanding repeatability from batch to batch synthesis. Remarkably, ASM OSCs with power conversion efficiency (PCE) beyond 13% were achieved by structure improvement of the electron donor and choosingY6as the electron acceptor. However, the fill factor (FF) is an obstacle that limits the further improvement of the PCE for these ASM OSCs. Herein, we focus on the FF improvement of recently reported ASM OSCs withBTR-Cl:Y6as the active layer by miscibility-induced active layer morphology optimization. The incorporation of fullerene derivatives, which have good miscibility with bothBTR-ClandY6, results in reduced bimolecular recombination and thus improved FF. In particular, whenca.5 wt% ofPC(71)BMwas added in the active layer, a FF of 77.11% was achieved without sacrificing the open circuit voltage (V-OC) and the short circuit current density (J(SC)), leading to a record PCE of 15.34% (certified at 14.7%) for ASM OSCs. We found that the optimized device showed comparable charge extraction, longer charge carrier lifetime, and slower bimolecular recombination rate compared with those of the control devices (w/o fullerene). Our results demonstrate that the miscibility driven regulation of active layer morphology by incorporation of a fullerene derivative delicately optimizes the active layer microstructures and improves the device performance, which brings vibrancy to OSC research.

19.46%-Efficiency all-polymer organic solar cells with excellent outdoor operating stability enabled by active layer reconstruction - Wu, Xiaohei; Xiao, Bo; Sun, Rui; Yang, Xinrong; Zhang, Meimei; Gao, Yuan; Xiao, Biao; Papkovskaya, Elizaveta D.; Luponosov, Yuriy; Brabec, Christoph; Min, Jie (Energy and Environmental Science, 2025)
Morphology control has been critical engineering in establishing rapid charge transfer channels and enhancing the solidification of the bulk microstructure, ultimately leading to improved device performance. Herein, we synergistically combined layer-by-layer (LbL) doctor-blading deposition with a multicomponent controlling strategy to achieve favorable active layer reconstruction and thus fabricated quaternary all-polymer solar cells (all-PSCs). Compared to the quaternary bulk-heterojunction (Q-BHJ) system based on PM6:D18-Cl:PY-SSe:PY-Cl, the quaternary LbL (Q-LbL) system based on (D18-Cl:PY-Cl)/(PM6:PY-SSe) can significantly improve the optical and electronic properties, ensure charge transfer and extraction, and reduce non-geminate recombination loss. Consequently, the rigid and flexible Q-LbL all-PSCs exhibit outstanding power conversion efficiencies of 19.46% and 17.02%, respectively. In particular, the Q-LbL system showed promising thermal and mechanical stability as well as outdoor operational stability. These findings highlight the potential of the Q-LbL processing strategy to simultaneously improve the efficiency and stability of all-PSCs, thereby paving the way for their practical applications.
CRIS-Team Scopus Importer:2025-01-31

2.5% efficient organic plastic solar cells - Shaheen, Sean E.; Brabec, Christoph; Sariciftci, N. Serdar; et al. (Applied Physics Letters, 2001)
We show that the power conversion efficiency of organic photovoltaic devices based on a conjugated polymer/methanofullerene blend is dramatically affected by molecular morphology. By structuring the blend to be a more intimate mixture that contains less phase segregation of methanofullerenes, and simultaneously increasing the degree of interactions between conjugated polymer chains, we have fabricated a device with a power conversion efficiency of 2.5% under AM1.5 illumination. This is a nearly threefold enhancement over previously reported values for such a device, and it approaches what is needed for the practical use of these devices for harvesting energy from sunlight. © 2001 American Institute of Physics.

29.9%-efficient, commercially viable perovskite/CuInSe2 thin-film tandem solar cells - Liang, Haoming; Feng, Jiangang; Rodríguez-Gallegos, Carlos D.; Krause, Maximilian; Wang, Xi; Alvianto, Ezra; Guo, Renjun; Liu, Haohui; Kothandaraman, Radha Krishnan; Carron, Romain; Tiwari, Ayodhya N.; Peters, Ian Marius; et al. (Joule, 2023)
Despite the ease of fabrication and no current matching constraint in mechanically stacked thin-film-based tandem solar cells, both electrical and optical losses still limit the performance of wide-band-gap perovskite semi-transparent solar cells in such tandem devices. The thin-film tandems using both perovskite and CuInSe2 (CIS) have not yet achieved optimal levels for commercial viability. Here, we present novel electrical and optical enhancement approaches to maximize the performance of perovskite front cells. We have introduced new electrical and optical techniques, using methyldiammonium diiodide and adjusting the optical interference spectrum. This resulted in a record efficiency of 20.2% (21.8% by J-V scan) for a semi-transparent perovskite cell and 81.5% average near-infrared transmittance. When paired with a CIS bottom cell, the tandem efficiency reached 29.9%. Techno-economic studies show that these tandems could deliver close to 2,000 Wh/m2 daily for certain locations and offer competitive electricity costs, ranging from 3 to 5 USDcents/kWh within ±30° latitude.
CRIS-Team Scopus Importer:2023-12-01
Keywords: 4-terminal tandem devices; carrier management; energy yield analysis; FDTD; finite-difference time-domian simulation; LCOE; levelized cost of electricity analysis; optical management; perovskite solar cells; perovskite/CIS tandem solar cells; techno-economic analysis; V

2D-3D heterostructure enables scalable coating of efficient low-bandgap Sn–Pb mixed perovskite solar cells - Zeng, Linxiang; Chen, Zongao; Qiu, Shudi; Hu, Jinlong; Li, Chaohui; Liu, Xianhu; Liang, Guangxing; Brabec, Christoph; Mai, Yaohua; Guo, Fei (Nano Energy, 2019)
Low-bandgap photovoltaic absorbers based on mixed tin-lead (Sn–Pb) halide perovskites offer promising opportunities to fabricate efficient multi-junction solar cells. However, the current Sn–Pb mixed perovskite solar cells (PSCs) were mainly prepared using lab-scale spin-coating, greatly hindering their application for large-area device fabrication. Here, we report a simple and robust methodology for scalable deposition of dense and uniform Sn–Pb mixed perovskite films by one-step blade coating. High quality perovskite films with different Sn–Pb ratios are readily prepared by vacuuming the freshly coated precursor films followed by an anneal process. Solar cells based on these bladed Sn–Pb mixed perovskite absorbers showed decent photovoltaic behaviors. Further enhancement of device performance was realized via surface defects passivation using phenethylammonium bromide (PEABr). It was found that the formation of a thin layer of 2D Ruddlesden-Popper perovskite on top of 3D bulk perovskite significantly suppressed charge recombination. As a consequence, the open-circuit voltage (VOC) of the solar cells (Eg = 1.35 eV) was dramatically lifted from 0.71 V to 0.78 V, yielding high efficiencies of over 15%. Moreover, notable improvement in shelf and moisture stability was observed due to the protection barrier of the 2D perovskite capping layer.
CRIS-Team Scopus Importer:2019-09-24
Keywords: 2D-3D heterostructure; Blade coating; Low bandgap; Perovskite solar cells; Sn–Pb mixed perovskite; Vacuum-assisted crystallization

3C-sic bulk sublimation growth on CVD hetero-epitaxial seeding layers - Schuh, Philipp; Litrico, G.; La Via, F.; Mauceri, M.; Wellmann, Peter (Materials Science Forum, 2017)
We report on the growth of bulk 3C-SiC by sublimation on epitaxial seeding layers (3C-SiC/Si) from chemical vapor deposition. We have reached a materials thickness of 0.85 mm and an area of 10.5 cm2 which can be enlarged further. The high crystalline quality is characterized by the absence of secondary polytype inclusions and the absence double position grain boundarie
Keywords: 3C-SiC; Cubic SiC; Epitaxy; Sublimation growth

4-Carboxyphenyl isothiocyanate as a Lewis base additive for efficient and stable perovskite solar cells - Fu, Shuai; Ma, Yuhui; Zhang, Zhiyuan; Xu, Yao; Zhang, Heyi; Xiao, Zihan; Zhang, Sihao; Xia, Ruidong (Synthetic Metals, 2023)
A high-quality perovskite film is of great significance for efficient and stable perovskite solar cells (PSCs). The use of additives to improve the crystallinity and morphology of perovskite films is an effective way to improve the performance of PSC devices. In this work, 4-carboxyphenyl isothiocyanate (CPIC) was used as an additive in perovskite films to improve the quality of the films. The results of FT-IR showed that the SCN- and -COOH groups with Lewis base in CPIC can coordinate with unpaired Pb2+ on the perovskite films to form Lewis acid-base adducts. The addition of CPIC can effectively improve the crystallinity and grain size of the perovskite films. The results showed that the short circuit current density (JSC) and fill factor (FF) of PSC devices increase significantly with the improvement of film quality, when the concentration of CPIC is 0.5 mg mL−1. These made the efficiency of the devices increase from 16.16 % to 18.19 %. Meanwhile, the introduction of the benzene ring in CPIC can improve the stability of the PSC devices. After aging at room temperature and 50 % humidity for 30 days, the device added with CPIC retained 61.9 % of the initial PCE. This work proves that using CPIC as an additive is an effective method to achieve efficient and stable PSCs.
CRIS-Team Scopus Importer:2023-01-13
Keywords: Crystallinity; Film morphology; Inverted perovskite solar cells; Lewis base additives

4H-1,2,6-Thiadiazin-4-one-containing small molecule donors and additive effects on their performance in solution-processed organic solar cells - Hermerschmidt, Felix; Kalogirou, Andreas S.; Min, Jie; Zissimou, Georgia A.; Tuladhar, Sachetan M.; Ameri, Tayebeh; Faber, Hendrik; Itskos, Grigorios; Choulis, Stelios A.; Anthopoulos, Thomas D.; Bradley, Donal D. C.; Nelson, Jenny; et al. (Journal of Materials Chemistry C, 2015)
The optical, electrochemical, morphological and transport properties of a series of thiadiazinone (acceptor) and (thienyl)carbazoles (donor) containing π-extended donor-acceptor-donors (D-A-D) are presented. Systematic variations in the number of the thienyl units, the choice of branched or straight alkyl side chains and the use of a processing additive demonstrate their use as electron donors in bulk heterojunction solar cells blended with fullerene acceptors. The best power conversion efficiency (PCE) of 2.7% is achieved by adding to the D-A-D 3:fullerene blend a polydimethylsiloxane (PDMS) additive, that improves the morphology and doubles the hole mobility within the D-A-D:fullerene blend.

9-Aryl-phenalenones: Bioinspired thermally reversible photochromic compounds for photoswitching applications in the pico-to milliseconds range - Bresolí-Obach, Roger; Massad, Walter A.; Abudulimu, Abasi; Lüer, Larry; Flors, Cristina; Luis, Javier G.; Rosquete, Laura I.; Grillo, Teresa A.; Anamimoghadam, Ommid; Bucher, Götz; Nonell, Santi (Dyes and Pigments, 2020)
Ultrafast photochromic molecules are being actively investigated to meet the demand for fast optical switching systems. Inspired on the irreversible cyclization of 9-phenylphenalenone plant metabolites to yield highly-coloured naphthoxanthenes for the purpose of defense against pathogens, aryl-substituted phenalenones have been developed that undergo a similar but reversible photochromic reaction. The lifetime of the naphthoxanthene photoisomer spans nine orders of magnitude, ranging from tens of picoseconds to tens of milliseconds depending on the electronic properties of the 9-aryl group.
CRIS-Team Scopus Importer:2020-12-25
Keywords: Chromene; Phenalenone; Photochromic; Photoswitch; β-phenyl quenching

A Bayesian Approach to Predict Solubility Parameters - Sanchez-Lengeling, Benjamin; Roch, Loïc; Perea Ospina, Jose Dario; Langner, Stefan; Brabec, Christoph; Aspuru-Guzik, Alan (Advanced Theory and Simulations, 2019)
Solubility is a ubiquitous phenomenon in many aspects of material science. While solubility can be determined by considering the cohesive forces in a liquid via the Hansen solubility parameters (HSP), quantitative structure-property relationship models are often used for prediction, notably due to their low computational cost. Here, gpHSP, an interpretable and versatile probabilistic approach to determining HSP, is reported. Our model is based on Gaussian processes, a Bayesian machine learning approach that provides uncertainty bounds to prediction. gpHSP achieves its flexibility by leveraging a variety of input data, such as SMILES strings, COSMOtherm simulations, and quantum chemistry calculations. gpHSP is built on experimentally determined HSP, including a general solvents set aggregated from the literature, and a polymer set experimentally characterized by this group of authors. In all sets, a high degree of agreement is obtained, surpassing well-established machine learning methods. The general applicability of gpHSP to miscibility of organic semiconductors, drug compounds, and in general solvents is demonstrated, which can be further extended to other domains. gpHSP is a fast and accurate toolbox, which could be applied to molecular design for solution processing technologies.
Keywords: machine learning; miscibility; organic materials; polymers; solubility

A Benchmark for Visual Identification of Defective Solar Cells in Electroluminescence Imagery - Buerhop-Lutz, Claudia; Deitsch, Sergiu; Maier, Andreas; Gallwitz, Florian; Berger, Stephan; Doll, Bernd; Hauch, Jens; Camus, Christian; Brabec, Christoph (35th European Photovoltaic Solar Energy Conference and Exhibition, 2018)
In this paper a dataset consisting of 2,426 solar cells extracted from high-resolution electroluminescence (EL) images is used for automated defect probability recognition. The collected images contain both functional and defective solar cells with varying degrees of degradation both in monocrystalline and polycrystalline solar modules. The images were labeled by expert who categorized the solar cells by the likelihood of a defect within each image. The labeled images can be used for development of computer vision and machine learning methods for automatic detection of different defects, like cracks, fracture interconnects, PID, and cell quality and for the purpose of predicting the power efficiency los
Keywords: EL Imaging; Machine Learning; Visual Inspection

A bilayer conducting polymer structure for planar perovskite solar cells with over 1,400 hours operational stability at elevated temperatures - Zhao, Yicheng; Heumueller, Thomas; Zhang, Jiyun; Luo, Junsheng; Kasian, Olga; Langner, Stefan; Kupfer, Christian; Liu, Bowen; Zhong, Yu; Elia, Jack; Osvet, Andres; Wu, Jianchang; et al. (Nature Energy, 2021)
The long-term stability of perovskite solar cells remains a challenge. Both the perovskite layer and the device architecture need to endure long-term operation. Here we first use a self-constructed high-throughput screening platform to find perovskite compositions stable under heat and light. Then, we use the most stable perovskite composition to investigate the stability of contact layers in solar cells. We report on the thermal degradation mechanism of transition metal oxide contact (for example, Ta-WOx/NiOx) and propose a bilayer structure consisting of acid-doped polymer stacked on dopant-free polymer as an alternative. The dopant-free polymer provides an acid barrier between the perovskite and the acid-doped polymer. The bilayer structure exhibits stable ohmic contact at elevated temperatures and buffers iodine vapours. The unencapsulated device based on the bilayer contact (with a MgF2 capping layer) retains 99% of its peak efficiency after 1,450 h of continuous operation at 65 degrees C in a N-2 atmosphere under metal-halide lamps. The device also shows negligible hysteresis during the entire ageing period.
CRIS-Team WoS Importer:2021-12-24

Abnormal strong burn-in degradation of highly efficient polymer solar cells caused by spinodal donor-acceptor demixing - Li, Ning; Perea, José Darío; Kassar, Thaer; Richter, Moses; Heumüller, Thomas; Matt, Gebhard; Hou, Yi; Güldal, Nusret Sena; Chen, Haiwei; Chen, Shi; Langner, Stefan; Berlinghof, Marvin; et al. (Nature Communications, 2017)
The performance of organic solar cells is determined by the delicate, meticulously optimized bulk-heterojunction microstructure, which consists of finely mixed and relatively separated donor/acceptor regions. Here we demonstrate an abnormal strong burn-in degradation in highly efficient polymer solar cells caused by spinodal demixing of the donor and acceptor phases, which dramatically reduces charge generation and can be attributed to the inherently low miscibility of both materials. Even though the microstructure can be kinetically tuned for achieving high-performance, the inherently low miscibility of donor and acceptor leads to spontaneous phase separation in the solid state, even at room temperature and in the dark. A theoretical calculation of the molecular parameters and construction of the spinodal phase diagrams highlight molecular incompatibilities between the donor and acceptor as a dominant mechanism for burn-in degradation, which is to date the major short-time loss reducing the performance and stability of organic solar cells.

Absence of Charge Transfer State Enables Very Low V-OC Losses in SWCNT:Fullerene Solar Cells - Classen, Andrej; Einsiedler, Lukas; Heumuelier, Thomas; Graf, Arko; Brohmann, Maximilian; Berger, Felix; Kahmann, Simon; Richter, Moses; Matt, Gebhard; Forberich, Karen; Zaumseil, Jana; Brabec, Christoph (Advanced Energy Materials, 2019)
Current state-of-the-art organic solar cells (OSCs) still suffer from high losses of open-circuit voltage (V-OC). Conventional polymer:fullerene solar cells usually exhibit bandgap to V-OC losses greater than 0.8 V. Here a detailed investigation of V-OC is presented for solution-processed OSCs based on (6,5) single-walled carbon nanotube (SWCNT): [6,6]-phenyl-C-71-butyric acid methyl ester active layers. Considering the very small optical bandgap of only 1.22 eV of (6,5) SWCNTs, a high V-OC of 0.59 V leading to a low E-gap/q - V-OC = 0.63 V loss is observed. The low voltage losses are partly due to the lack of a measurable charge transfer state and partly due to the narrow absorption edge of SWCNTs. Consequently, V-OC losses attributed to a broadening of the band edge are very small, resulting in V-OC,V-SQ - V-OC,V-rad = 0.12 V. Interestingly, this loss is mainly caused by minor amounts of SWCNTs with smaller bandgaps as well as (6,5) SWCNT trions, all of which are experimentally well resolved employing Fourier transform photocurrent spectroscopy. In addition, the low losses due to band edge broadening, a very low voltage loss are also found due to nonradiative recombination, Delta V-OC,V-nonrad = 0.26 V, which is exceptional for fullerene-based OSCs.
Keywords: all-carbon absorbers; charge transfer state; organic photovoltaics; single-walled carbon nanotubes; V-OC loss analysis

Absorption mapping of doping level distribution in n-type and p-type 4H-SiC and 6H-SiC - Weingärtner, Roland; Bickermann, Matthias; Bushevoy, S.; Hofmann, Heinz-Dieter; Rasp, M.; Straubinger, Thomas; Wellmann, Peter; Winnacker, Albrecht (Materials Science and Engineering B-Advanced Functional Solid-State Materials, 2001)
An optical characterization method for determination of spatial doping level concentration in n-type 4H-SiC and p-type GH-SIC is discussed. The absorption bands of free charge carriers at 460 nm in n-type 4H-SiC are used to determine its doping concentration. In p-type 6H-SiC, the band edge related absorption at 410 nm is a measure for the doping concentration. In both cases, Hall measurements are performed fur calibration. Various examples of SiC-wafer mappings are shown and the relationships to crystal growth conditions, i.e. control of duping level and distribution, are investigated. (C) 2001 Elsevier Science S.A. All rights reserved.
Keywords: Silicon carbide; Absorption mapping; Polytypes; Doping level determination; Crystal growth

Absorption measurements and doping level evaluation in n-type and p-type 4H-SiC and 6H-SiC - Weingärtner, Roland; Bickermann, Matthias; Hofmann, Heinz-Dieter; Rasp, M.; Straubinger, Thomas; Wellmann, Peter; Winnacker, Albrecht (Materials Science Forum, 2001)
An optical characterization method based on the fundamental absorption bands in SiC is presented for determination of the spatial distribution of doping level concentration in n-type 4H- and 6H-SiC and p-type (Al, B) 6H-SiC. Band gap related absorption has been calculated numerically taking into account band filling, band shrinkage and band tailing effects and has been compared with experimental data. In addition, below band gap absorption transitions in n-type 4H-SiC and p-type (B) 6H-SiC at 460nm and 730nm, respectively, have been investigated. Calibration plots correlating these absorption bands with the charge carrier concentration have been determined and the application for mapping of the doping level distribution in SiC wafers will be demonstrate
Keywords: Absorption Band; Absorption Mapping; Doping Level Determination; Polytype

Accelerated degradation of Al3+ doped ZnO thin films using damp heat test - Litzov, Ivan; Azimi, Seyed Hamed; Matt, Gebhard; Kubis, Peter; Stubhan, Tobias; Popov, Georgi; Brabec, Christoph (Organic Electronics, 2014)
Two different types of aluminum-doped zinc oxide (AZO) thin films were fabricated using low cost sol-gel technique. By applying damp heat testing, the optical and electrical properties of those films were investigated under the influence of accelerated degradation from moisture or moisture vapor. Complementary measurements of optical transmittance, work function, and conductivity allowed exploring the degradation of AZO thin films and the corresponding OPV devices. We found that optical properties like transmittance, absorption coefficient, and band gap are not influenced by temperature and moisture. However, an increase in the work function, and a decrease in the conductivity of AZO films were observed upon damp heat exposure indicating the formation of a barrier or depletion layer at the metal oxide semiconductor interface. © 2013 Elsevier B.V. All rights reserved.
Keywords: Aluminum-doped zinc oxide; Conductivity; Damp heat test; Work function

Accelerated lifetime testing of thin-film solar cells at high irradiances and controlled temperatures - Burlafinger, Klaus; Strohm, Sebastian; Joisten, Christoph; Woiton, Michael; Classen, Andrej; Hepp, Johannes; Heumüller, Thomas; Brabec, Christoph; Vetter, Andreas (Progress in Photovoltaics, 2021)
Within this study, we investigate the intrinsic photostability of thin-film solar cells, here organic photovoltaic cells. Since degradation under natural sun light proceeds within the timeframe of months and years, the process needs to be speeded up for fast material analysis and screening, using high-concentration accelerated lifetime testing (high-C ALT). For this purpose, we established setups allowing irradiances of up to 730 sun equivalents (SE). One key finding of our study is that accelerating the testing procedure by such large intensities is possible but a precise measurement and control of the solar cell temperature is absolutely essential. Accordingly, we developed an innovative method of determining the temperature of the active layer which offers significant advantages over commonly used measurement methods. Furthermore, it was found that the degradation process under high illumination densities can be well described by a stretched exponential law. We demonstrate that the temperature kinetics of P3HT:PCBM was found to be Arrhenius governed with an activation energy of 27.2 kJ/mol under continuous illumination of 300 SE. Finally, it was shown that the velocity of light-induced degradation of short-circuit current depends linearly on the used irradiance dose at a given temperature starting from normal illumination conditions up to at least 300 SE. This makes high-C ALT a very valuable tool for swift screening of the lifetime of novel thin-film solar cells and materials.
CRIS-Team Scopus Importer:2021-11-26
Keywords: accelerated degradation; high irradiances; temperature check

Accelerating Photostability Evaluation of Perovskite Films through Intelligent Spectral Learning-Based Early Diagnosis - Liu, Ziyi; Zhang, Jiyun; Rao, Gaofeng; Peng, Zijian; Huang, Yixing; Arnold, Simon; Liu, Bowen; Deng, Can; Li, Chen; Li, Heng; Zhi, Hanxiang; Zhang, Zhi; et al. (ACS Energy Letters, 2024)
Obtaining highly stable metal-halide perovskites is crucial for the commercialization of perovskite solar cells. However, current methods for evaluating perovskite stability mainly rely on a time-consuming and resource-intensive aging process. Here, we demonstrate a spectral learning-based methodology that enables the prediction of perovskite stability by leveraging the features in photoluminescence and absorption spectra of fresh perovskite films. This methodology circumvents the long-term aging process by combining a custom-developed spectral feature extraction algorithm and an integrated voting machine learning model. By integration of the early diagnosis program with high-throughput experiments, the prediction accuracy for stable perovskites exceeds 86% in 160 fresh samples. The universality is further examined by another batch of 224 fresh samples fabricated through different processing conditions. Finally, the early diagnosis of perovskite films is successfully translated to enhanced stability in perovskite solar cells. Our work provides a new pathway to accelerate the discovery and development of stable perovskite films.
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Accelerating the discovery of materials for clean energy in the era of smart automation - Tabor, Daniel P.; Roch, Loic M.; Saikin, Semion K.; Kreisbeck, Christoph; Sheberla, Dennis; Montoya, Joseph H.; Dwaraknath, Shyam; Aykol, Muratahan; Ortiz, Carlos; Tribukait, Hermann; Amador-Bedolla, Carlos; Brabec, Christoph; et al. (NATURE REVIEWS MATERIALS, 2018)
The discovery and development of novel materials in the field of energy are essential to accelerate the transition to a low-carbon economy. Bringing recent technological innovations in automation, robotics and computer science together with current approaches in chemistry, materials synthesis and characterization will act as a catalyst for revolutionizing traditional research and development in both industry and academia. This Perspective provides a vision for an integrated artificial intelligence approach towards autonomous materials discovery, which, in our opinion, will emerge within the next 5 to 10 years. The approach we discuss requires the integration of the following tools, which have already seen substantial development to date: high-throughput virtual screening, automated synthesis planning, automated laboratories and machine learning algorithms. In addition to reducing the time to deployment of new materials by an order of magnitude, this integrated approach is expected to lower the cost associated with the initial discovery. Thus, the price of the final products (for example, solar panels, batteries and electric vehicles) will also decrease. This in turn will enable industries and governments to meet more ambitious targets in terms of reducing greenhouse gas emissions at a faster pace.

Acceptor-hydrogen interaction in ternary III-V semiconductors - Burchard, A.; Deicher, M.; Forkel-Wirth, D.; Freidinger, J.; Kerle, T.; Magerle, R.; Pfeiffer, W.; Prost, W.; Wellmann, Peter; Winnacker, Albrecht (Materials Science Forum, 1995)
The formation of acceptor-hydrogen complexes has been studied in Cd doped ternary III-V compounds AlGaAs, InGaAs and GaInP. Using the perturbed gamma gamma angular correlation technique (PAC) with radioactive Cd-111m accepters, the interaction between the Cd accepters and H introduced by low energy implantation (100 eV) was examined quantitatively. The observed formation probability of Cd-H complexes and their hyperfine interaction parameters are compared with the ones observed for the binary compounds GaAs, AlAs, InAs, InP, and GaP.
Keywords: AlGaAs; InGaAs; GaInP; hydrogen; PAC

Acenequinocumulenes: Lateral and vertical π-extended analogs of tetracyanoquinodimethane (TCNQ) - Gruber, Marco; Padberg, Kevin; Min, Jie; Waterloo, Andreas; Hampel, Frank; Maid, Harald; Ameri, Tayebeh; Brabec, Christoph; Tykwinski, Rik (Chemistry - A European Journal, 2017)
We have designed a series of molecules and developed synthetic methodology that allows for the inclusion of structural diversity along both the lateral and vertical axes of the basic TCNQ skeleton. In the lateral direction, benzoannulation extends the π-system through (hetero)acene formation, while incorporation of a [3]cumulene increases delocalization vertically. The potential of these new molecules as semiconductors is explored through UV-vis spectroscopy, cyclic voltammetry, X-ray crystallography, thin film formation, and mobility measurements (via space charge limited current measurements
Keywords: pentacenes; donor-acceptor; organic materials; cumulenes; synthetic methodology

Achieving efficient and stabilized organic solar cells by precisely controlling the proportion of copolymerized units in electron-rich polymers - Xie, Qian; Cui, Yongjie; Chen, Zeng; Zhang, Ming; Liu, Chao; Zhu, Haiming; Liu, Feng; Brabec, Christoph; Liao, Xunfan; Chen, Yiwang (Nanoscale, 2022)
A series of random polymers based on the donor polymer PM6 were designed from the perspective of regulating the surface electrostatic potential (ESP) distribution of the polymers and applied in organic solar cells (OSCs). Random polymers with different ESPs were obtained by introducing structural units of polymer PM6 into the polymer structure as the third unit. The simulation results showed that the random polymers feature a wider electron-donating region after the introduction of BDT units, indicating a more efficient charge generation probability. Benefiting from the optimized morphology of the active layer and the stronger interaction between the donor and the acceptor in the active layer, the device exhibited the best charge transport efficiency and lower charge recombination after the introduction of 5% BDT units, and a high power conversion efficiency (PCE) of 16.76% was achieved. In addition, OSC devices based on random polymers incorporating 5% BDT units exhibit excellent device stability. In contrast, the devices based on random polymers after the introduction of BDD units showed a much lower PCE of around 13% due to the inferior charge generation and charge transport. This work not only provides a new perspective for the molecular design of efficient random polymers, but also demonstrates that the OSC devices based on random polymers can still achieve better stability.
CRIS-Team WoS Importer:2022-12-09

Achieving efficient inverted perovskite solar cells with excellent electron transport and stability by employing a ladder-conjugated perylene diimide dimer - Wang, Helin; Yang, Fu; Xiang, Yuren; Ye, Shuai; Peng, Xiao; Song, Jun; Qu, Junle; Wong, Wai Yeung (Journal of Materials Chemistry A, 2019)
The lack of organic electron transport materials (ETM) with excellent electron transport and device stability is an important problem for the development and commercialization of perovskite solar cells (PSCs). Herein, a ladder-conjugated perylene diimide dimer containing an indacenodithiophene unit, namely IDTT2FPDI, was synthesized in two steps with high yields. In addition, IDTT2FPDI exhibits suitable energy levels, high electron mobility, and an excellent hydrophobicity because of its multiple fused thiophene rings and large ladder-conjugated framework. Compared with inverted PSCs which typically use PCBM as a single electron transport layer (ETL), the device utilizing IDTT2FPDI/PCBM as a double ETL showed a better power conversion efficiency (PCE) of 19.4%. Moreover, the double ETL-based devices exhibited superior stability compared with the single ETL-based devices due to the hydrophobicity of the IDTT2FPDI layer. These results highlight the potential of employing ladder-conjugated PDI dimers as ETMs to obtain high-efficiency and stable PSCs, which shows promise for the development of PSCs.
CRIS-Team Scopus Importer:2019-11-08

Achieving Efficient Thick Film All-polymer Solar Cells Using a Green Solvent Additive - Li, Zhen Ye; Zhong, Wen Kai; Ying, Lei; Li, Ning; Liu, Feng; Huang, Fei; Cao, Yong (Chinese Journal of Polymer Science, 2019)
Advances in organic photovoltaic technologies have been geared toward industrial high-throughput printing manufacturing, which requires insensitivity of photovoltaic performance regarding to the light-harvesting layer thickness. However, the thickness of light-harvesting layer for all polymer solar cells (all-PSCs) is often limited to about 100 nm due to the dramatically decreased fill factor upon increasing film thickness, which hampers the light harvesting capability to increase the power conversion efficiency, and is unfavorable for fabricating large-area devices. Here we demonstrate that by tuning the bulk heterojunction morphology using a non-halogenated solvent, cyclopentyl methyl ether, in the presence of a green solvent additive of dibenzyl ether, the power conversion efficiency of all-PSCs with photoactive layer thicknesses of over 500 nm reached an impressively high value of 9%. The generic applicability of this green solvent additive to boost the power conversion efficiency of thick-film devices is also validated in various bulk heterojunction active layer systems, thus representing a promising approach for the fabrication of all-PSCs toward industrial production, as well as further commercialization.
CRIS-Team Scopus Importer:2019-12-10
Keywords: Dibenzyl ether; Green solvent additive; Thick-film all-polymer solar cell

Achieving High External Quantum Efficiency for ITIC-Based Organic Solar Cells with Negligible Homo Energy Offsets - Du, Huijun; An, Kang; Wang, Rong; Yin, Zhipeng; Peng, Feng; Lüer, Larry; Brabec, Christoph; Ying, Lei; Li, Ning (Advanced Energy Materials, 2024)
Minimizing energy loss in organic solar cells (OSCS) is critical for attaining high photovoltaic performance. Among the parameters that correlated to photovoltaic performance, the energy offsets between donor–acceptor pairs play a vital role in photoelectric conversion processes. For so far reported a large number of non-fullerene acceptors (NFAs), only Y6 and its derivatives can achieve external quantum efficiencies (EQEs) over 80% with negligible energy offsets when combined with polymeric donors. Thus, understanding the relationship between energy offsets and energy losses in representative NFAs is the key to further enhancing the efficiency of OSCs. In this study, a series of wide-bandgap polymer donors based on pyrrolo[3,4-f]benzotriazole-5,7(6H)-dione (TzBI) and benzo[1,2-c:4,5-c′] dithiophene-4,8-dione building blocks are combined with representative NFAs, including ITIC and Y6, to gain deep insights into their photovoltaic performances and related energy losses. Outstanding EQEs (≈70%) and suppressed non-radiative recombination are achieved at negligible energy offsets. Moreover, it is noted that a prolonged exciton lifetime of acceptor is not essential to obtain high EQEs in OSCs with negligible energy offsets. Eventually, ITIC derivatives with high electroluminescence efficiencies and near-infrared absorptions have the potential to be assembled to obtain high-efficiency OSCs.
CRIS-Team Scopus Importer:2024-02-16
Keywords: energy offsets; external quantum efficiency; non-fullerene acceptors; non-radiative energy loss

Achieving over 17% efficiency of ternary all-polymer solar cells with two well-compatible polymer acceptors - Sun, Rui; Wang, Wei; Yu, Han; Chen, Zeng; Xia, Xinxin; Shen, Hao; Guo, Jing; Shi, Mumin; Zheng, Yina; Wu, Yao; Yang, Wenyan; Wang, Tao; et al. (Joule, 2021)
The field of all-polymer solar cells (all-PSCs) has experienced rapid development during the past few years, mainly driven by the design of efficient polymer acceptors (PAs). However, the polymer/polymer blend systems still lag far behind polymer/small molecule acceptor counterparts in power conversion efficiencies (PCEs). Here, we designed a near-infrared PA PY2F-T and paired it with polymer donor PM6 to fabricate all-PSCs with 15.0% PCE. Afterwards, PYT as the third component was introduced into the PM6:PY2F-T host system. Because of the complementary absorption bands and finely tuned microstructures of the ternary blend, the PCE is improved up to 17.2%, with the external quantum efficiency over 80% in visible and near-infrared spectral regions. Impressively, the ternary blend exhibited less energy loss, better light-soaking and photo-thermal stabilities than did the corresponding binary systems. This work promotes the development of high-performance ternary all-polymer systems and heralds a brighter future for accelerating the possible applications of all-PSCs.
CRIS-Team Scopus Importer:2021-07-09
Keywords: absorption coefficient; all-polymer solar cells; energy loss; polymer acceptor; stability

A combination of Al-doped ZnO and a conjugated polyelectrolyte interlayer for small molecule solution-processed solar cells with an inverted structure - Min, Jie; Zhang, Hong; Stubhan, Tobias; Luponosov, Yuriy N.; Kraft, Mario; Ponomarenko, Sergei A.; Ameri, Tayebeh; Scherf, Ullrich; Brabec, Christoph (Journal of Materials Chemistry A, 2013)
We successfully demonstrate a smart strategy to use aluminum doped ZnO (AZO) and the thiophene-based conjugated polyelectrolyte P3TMAHT as an interfacial layer in small molecule solution-processed inverted solar cells. Modification of AZO with a thin P3TMAHT layer increases the photovoltaic properties of the inverted cell as a result of reduction in the work function of the cathode with well aligned frontier orbital energy levels for efficient charge transport and reduced surface recombination. The inverted device achieved 16% performance improvement dominantly by recapturing part of the Voc losses when going from conventional to the inverted architecture. In addition, the inverted device using the AZO/P3TMAHT interlayer shows improved device stability in air compared to conventional devices.
Keywords: Aluminum-doped ZnO; Conjugated polyelectrolytes; Frontier orbital energies; Inverted architectures; Inverted solar cells; Photovoltaic property; Solution-processed; Surface recombinations Engineering controlled terms: Molecules; Polyelectrolytes; Zinc oxide Engineering main heading: Solar cells

A comparison between state-of-the-art 'gilch' and 'sulphinyl' synthesised MDMO-PPV/PCBM bulk hetero-junction solar cells - Munters, T.; Martens, T.; Goris, L.; Vrindts, V.; Manca, J.; Lutsen, L.; De Ceuninck, W.; Vanderzande, D.; De Schepper, L.; Gelan, J.; Sariciftci, Niyazi Serdar; Brabec, Christoph (Thin Solid Films, 2002)
To obtain photovoltaic devices based on electron donating conjugated polymers with a higher efficiency, a major breakthrough was realised by mixing the polymers with a suitable electron acceptor, thereby enhancing the rate for photo-induced charge generation by several orders. State-of-the-art organic bulk hetero-junction photovoltaic cells are based on an interpenetrating donor-acceptor network in the bulk to form efficient nanostructured p-n junctions in the organic materials. Devices made with 'Gilch' poly(2-methoxy-5-(3′,7′-dimethyl-octyloxy))-p-phenylene vinylene, (MDMO-PPV), as an electron donor and (6,6)-phenyl-C-butyric-acid (PCBM) (a soluble C60 derivative) as an electron acceptor yielded the highest efficiency until now in this class of devices. A power conversion efficiency of approximately η≥2.5% (electrical power out/incident light power) under AM 1.5 illumination was reported. The 'gilch' route is a direct synthetic route. The 'sulphinyl' route is a promising, indirect precursor-route towards MDMO-PPV. Due to the non-symmetric monomer, so-called 'head-to-head' and 'tail-to-tail' additions are excluded to a higher level in comparison to the 'gilch' route. This difference between both materials makes them interesting candidates to compare them in the state-of-the-art photovoltaic devices. Preliminary results indicate that the 'sulphinyl' MDMO-PPV/PCBM bulk hetero-junction solar cells attain a power conversion efficiency of nearly η=3% (electrical power out/incident light power), have a higher fill factor, incident photon per converted electron value (IPCE) and short circuit current. It is indicated that the observed solar cell characteristics are related to the defect level of the conjugated polymer used. © 2002 Elsevier Science B.V. All rights reserved.
Keywords: Gilch; Hetero-junction solar cells; MDMO-PPV; OCICIO; Organic photovoltaics; Organic solar cell; PCBM; PPV; Sulphinyl

A conformally bonded molecular interface retarded iodine migration for durable perovskite solar cells - Yuan, Ligang; Zhu, Weiya; Zhang, Yiheng; Li, Yuan; Chan, Christopher C. S.; Qin, Minchao; Qiu, Jianhang; Zhang, Kaicheng; Huang, Jiaxing; Wang, Jiarong; Luo, Huiming; Zhang, Zheng; et al. (Energy and Environmental Science, 2023)
State-of-the-art n-i-p perovskite solar cells (PSCs) suffer from stability issues due to ionic interdiffusion. Herein, by enlarging the indacenodithiophene π-bridge donor (D′) to combine with the methoxy triphenylamine donor (D) and benzothiadiazole acceptor (A), three linear molecules termed L1, L2 and L3 with a D-A-D′-A-D structure are developed as dopant-free hole transport materials (HTMs). The π-bridge extension with active sites for coordination leverages the intramolecular dipole effect and intermolecular packing effect, resulting in a conformally bonded ultrathin interface with compact and uniform coverage (∼60 nm) to retard iodine migration and protect the buried perovskite. The unencapsulated L3-PSC (ITO/SnO2/perovskite/L3/MoO3/Au) achieved an impressive PCE of 22.61% (certified 21.79%, 0.0525 cm2). Ultrafast laser spectroscopy reveals that L-series molecules have a sequential reduction of photoexcited energy disorder to illustrate the structure-performance-stability relationship. L3-PSC maintains over 85% of the initial efficiency after 500 h at 85 °C maximum power point tracking (MPP) and enables the possibility of using small molecules to stabilize n-i-p PSCs.
CRIS-Team Scopus Importer:2023-05-05

A Cost-Effective, Aqueous-Solution-Processed Cathode Interlayer Based on Organosilica Nanodots for Highly Efficient and Stable Organic Solar Cells - Cui, Mengqi; Li, Dan; Du, Xiaoyan; Li, Na; Rong, Qikun; Li, Ning; Shui, Lingling; Zhou, Guofu; Wang, Xinghua; Brabec, Christoph; Nian, Li (Advanced Materials, 2020)
The performance and industrial viability of organic photovoltaics are strongly influenced by the functionality and stability of interface layers. Many of the interface materials most commonly used in the lab are limited in their operational stability or their materials cost and are frequently not transferred toward large-scale production and industrial applications. In this work, an advanced aqueous-solution-processed cathode interface layer is demonstrated based on cost-effective organosilica nanodots (OSiNDs) synthesized via a simple one-step hydrothermal reaction. Compared to the interface layers optimized for inverted organic solar cells (i-OSCs), the OSiNDs cathode interlayer shows improved charge carrier extraction and excellent operational stability for various model photoactive systems, achieving a remarkably high power conversion efficiency up to 17.15%. More importantly, the OSiNDs’ interlayer is extremely stable under thermal stress or photoillumination (UV and AM 1.5G) and undergoes no photochemical reaction with the photoactive materials used. As a result, the operational stability of inverted OSCs under continuous 1 sun illumination (AM 1.5G, 100 mW cm−2) is significantly improved by replacing the commonly used ZnO interlayer with OSiND-based interfaces.
CRIS-Team Scopus Importer:2020-08-21
Keywords: cathode interlayers; device stability; organic photovoltaics; organosilica nanodots; photostability

A Cross-Linked Interconnecting Layer Enabling Reliable and Reproducible Solution-Processing of Organic Tandem Solar Cells - Liu, Chao; Du, Xiaoyan; Gao, Shuai; Classen, Andrej; Osvet, Andres; He, Yakun; Mayrhofer, Karl; Li, Ning; Brabec, Christoph (Advanced Energy Materials, 2020)
The performance of tandem organic solar cells (OSCs) is directly related to the functionality and reliability of the interconnecting layer (ICL). However, it is a challenge to develop a fully functional ICL for reliable and reproducible fabrication of solution-processed tandem OSCs with minimized optical and electrical losses, in particular for being compatible with various state-of-the-art photoactive materials. Although various ICLs have been developed to realize tandem OSCs with impressively high performance, their reliability, reproducibility, and generic applicability are rarely analyzed and reported so far, which restricts the progress and widespread adoption of tandem OSCs. In this work, a robust and fully functional ICL is developed by incorporating a hydrolyzed silane crosslinker, (3-glycidyloxypropyl)trimethoxysilane (GOPS), into poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS), and its functionality for reliable and reproducible fabrication of tandem OSCs based on various photoactive materials is validated. The cross-linked ICL can successfully protect the bottom active layer against penetration of high boiling point solvents during device fabrication, which widely broadens the solvent selection for processing photoactive materials with high quality and reliability, providing a great opportunity to continuously develop the tandem OSCs towards future large-scale production and commercialization.
CRIS-Team Scopus Importer:2020-02-25
Keywords: (3-glycidyloxypropyl)trimethoxysilane; cross-linking; interconnecting layer; organic tandem solar cells; solution-processing

A data fusion approach to optimize compositional stability of halide perovskites - Sun, Shijing; Tiihonen, Armi; Oviedo, Felipe; Liu, Zhe; Thapa, Janak; Zhao, Yicheng; Hartono, Noor Titan P.; Goyal, Anuj; Heumüller, Thomas; Batali, Clio; Encinas, Alex; Yoo, Jason J.; et al. (Matter, 2021)
Search for resource-efficient materials in vast compositional spaces is an outstanding challenge in creating environmentally stable perovskite semiconductors. We demonstrate a physics-constrained sequential learning framework to subsequently identify the most stable alloyed organic-inorganic perovskites. We fuse data from high-throughput degradation tests and first-principle calculations of phase thermodynamics into an end-to-end Bayesian optimization algorithm using probabilistic constraints. By sampling just 1.8% of the discretized CsxMAyFA1−x−yPbI3 (MA, methylammonium; FA, formamidinium) compositional space, perovskites centered at Cs0.17MA0.03FA0.80PbI3 show minimal optical change under increased temperature, moisture, and illumination with >17-fold stability improvement over MAPbI3. The thin films have 3-fold improved stability compared with state-of-the-art multi-halide Cs0.05(MA0.17FA0.83)0.95Pb(I0.83Br0.17)3, translating into enhanced solar cell stability without compromising conversion efficiency. Synchrotron-based X-ray scattering validates the suppression of chemical decomposition and minority phase formation achieved using fewer elements and a maximum of 8% MA. We anticipate that this data fusion approach can be extended to guide materials discovery for a wide range of multinary systems. Despite recent intensive efforts to improve the environmental stability of halide perovskite materials for energy harvesting and conversion, traditional trial-and-error explorations face bottlenecks in the navigation of vast chemical and compositional spaces. We develop a closed-loop optimization framework that seamlessly marries data from first-principle calculations and high-throughput experimentation into a single machine learning algorithm. This framework enables us to achieve rapid optimization of compositional stability for CsxMAyFA1−x−yPbI3 perovskites while taking the human out of the decision-making loop. We envision that this data fusion approach is generalizable to directly tackle challenges in designing multinary materials, and we hope that our successful showcase on perovskites will encourage researchers in other fields to incorporate knowledge of physics into the search algorithms, applying hybrid machine learning models to guide discovery of materials in high-dimensional spaces. Data fusion combines first-principle calculations and high-throughput experimentation into an end-to-end closed-loop optimization framework, allowing an accelerated search of alloyed halide perovskites in a combinatorial space without human intervention.
CRIS-Team Scopus Importer:2021-03-05
Keywords: Bayesian optimization; data fusion; density-functional theory; energy materials; high-throughput experimentation; machine learning; MAP4: Demonstrate; perovskite stability

Additional pipework opens up transistor applications for SiC - Wellmann, Peter (Compound Semiconductor, 2005)
The use of modified physical vapor transport (MPVT), an alternative approach for silicon carbide growth to improve LED and Schottky-diode performance is described. MVPT uses an additional gas pipe to fine-tune the gas-phase composition and also achieves vastly improved aluminium-doping profiles in SiC. The MPVT process could also increase the yield of 4H-SiC substrates through polytype control and also lead to heavily phosphorus-doped substrates that reduce substrate resistance, and thereby enabling the production of low-power-loss Schottky diodes. The approach is also unaffected by the additional gas flux, with even the addition of propane or silane producing no change to a chemical vapor deposition (CVD
Keywords: Silicon carbide | Epitaxial growth | threading screw

A digital twin to overcome long-time challenges in photovoltaics - Lüer, Larry; Peters, Ian Marius; Smith, Ana-Suncana; Dorschky, Eva; Eskofier, Björn; Liers-Bergmann, Frauke; Franke, Jörg; Sjarov, Martin; Brossog, Matthias; Guldi, Dirk Michael; Maier, Andreas; Brabec, Christoph (Joule, 2024)
The recent successes of emerging photovoltaics (PVs) are largely driven by innovations in material science. However, closing the gap to commercialization still requires significant progress to match contradicting requirements, such as performance, longevity, and recyclability. In this perspective, we envision the layout of a digital twin for PV materials able to provide the necessary acceleration of innovation. The layout combines machine learning approaches, as performed in materials acceleration platforms (MAPs), with physical models and digital twin concepts used in engineering. This layout will allow the use of high-throughput (HT) experimentation in MAPs to improve the parametrization of quantum chemical and solid-state models. In turn, the improved and generalized models can be used to obtain the crucial structural parameters. HT experimentation will thus yield a detailed understanding of generally valid structure-property relationships. We discuss the current state of the enabling technologies, namely fast scale-bridging surrogate models and large-scale optimization under uncertainty, and identify promising approaches for further development.<br
Keywords: digital twin; emerging photovoltaics; artificial intelligence; multi-scale simulations; optimization; high-throughput methods; materials acceleration platforms

Adjusting the energy of interfacial states in organic photovoltaics for maximum efficiency - Gasparini, Nicola; Camargo, Franco V.A.; Frühwald, Stefan; Nagahara, Tetsuhiko; Classen, Andrej; Roland, Steffen; Wadsworth, Andrew; Gregoriou, Vasilis G.; Chochos, Christos L.; Neher, Dieter; Salvador, Michael; Baran, Derya; et al. (Nature Communications, 2021)
A critical bottleneck for improving the performance of organic solar cells (OSC) is minimising non-radiative losses in the interfacial charge-transfer (CT) state via the formation of hybrid energetic states. This requires small energetic offsets often detrimental for high external quantum efficiency (EQE). Here, we obtain OSC with both non-radiative voltage losses (0.24 V) and photocurrent losses (EQE > 80%) simultaneously minimised. The interfacial CT states separate into free carriers with ≈40-ps time constant. We combine device and spectroscopic data to model the thermodynamics of charge separation and extraction, revealing that the relatively high performance of the devices arises from an optimal adjustment of the CT state energy, which determines how the available overall driving force is efficiently used to maximize both exciton splitting and charge separation. The model proposed is universal for donor:acceptor (D:A) with low driving forces and predicts which D:A will benefit from a morphology optimization for highly efficient OSC.
CRIS-Team Scopus Importer:2021-04-02

Advanced Electronics – Materials, Devices and System Applications (with Special Topic on Disperse Systems for Printable Electronics), Proceedings of the 3rd Chinese-German Summer School in Erlangen - Wellmann, Peter; Feng, Zhibiao; Shi, Guoyong (2009)

Advanced Light Management for Encapsulated Silicon Solar Cells: An Antireflective Textured Film with a Down-Shifting Lead-free Perovskite Cs2AgxNa1-xBiyIn1-yCl6 Phosphor - Kong, Mengqin; Raievska, Oleksandra; Stroyuk, Oleksandr; Barabash, Anastasia; Wu, Zhenni; Tian, Jingjing; Erban, Christof; Osvet, Andres; Batentschuk, Miroslaw; Brabec, Christoph (ACS Applied Materials and Interfaces, 2024)
Light management (LM) is the key to the encapsulation of high-performance silicon (Si) photovoltaic devices (PVs). In this work, simulation analyses provide meaningful insights into optical losses and guide the improvement of the PV performance of the encapsulated silicon solar cells (Encap-Si SCs). An antireflective layer, textured polydimethylsiloxane (PDMS), is designed to reduce reflection losses, especially at a lower illumination intensity, thereby achieving an improvement of 10.89% in the short-current density (JSC) and hence 12.67% in the power conversion efficiency (PCE) when illuminated at an incident angle of 60°. Subsequently, a luminescence down-shifting material, lead-free Cs2AgxNa1-xBiyIn1-yCl6 (CANBIC) double perovskite phosphor, is incorporated into the PDMS film to further enhance the energy yield in the ultraviolet (UV) region. The textured PDMS film with an optimized CANBIC content ultimately achieves a significant improvement in PCE from 21.770 to 23.136%. This enhancement is attributed to the increase in JSC by 2.381 mA/cm2 due to the reduced reflection losses (by antireflective PDMS) and down-converted UV energy (by CANBIC), providing a remarkable advance in LM toward highly efficient encapsulated PVs.
CRIS-Team Scopus Importer:2024-08-23
Keywords: antireflective layer; down-shifting layer; encapsulated Si solar cell; lead-free perovskite phosphor; optical simulation

Advances in In Situ SiC Growth Analysis Using Cone Beam Computed Tomography - Salamon, Michael; Arzig, Matthias; Uhlmann, Norman; Wellmann, Peter (Materials Science Forum, 2019)
Computed Tomography is becoming a valuable method for the in-situ monitoring of vapor grown silicon carbide single crystals [1]. Already the two-dimensional X-ray radiography has shown the potential of surveilling the growth process [2] and its characteristic features like the evolution of the facet, the crystal volume or the source material structure from one imaging plane. Even though the demands on imaging capability of the applied X-ray components used for a tomographic analysis are higher than for two-dimensional imaging, the extension of this method to the third dimension is highly beneficial. It allows investigating the full geometry and three-dimensional location of the features and by this provides a more accurate analysis. In this contribution we present the physical characteristics and the latest advances of our technique for the visualization of facets.
Keywords: 3D In Situ Analysis; Computed Tomography; PVT Growth Process Surveillance

Advances in Lead-Free Perovskite Single Crystals: Fundamentals and Applications - Tailor, Naveen Kumar; Kar, Shaoni; Mishra, Pranjal; These, Albert; Kupfer, Christian; Hu, Hanlin; Awais, Muhammad; Saidaminov, Makhsud; Dar, M. Ibrahim; Brabec, Christoph; Satapathi, Soumitra (ACS Materials Letters, 2021)
With rapid progress in the deployment of metal halide perovskites in various device applications such as solar cells, light-emitting devices, field-effect transistors, photodetectors, etc., the next eminent focus is on the single crystals of these materials. With a lack of grain boundaries and low trap densities, remarkably long charge carrier diffusion lengths, and high ambient and operational stabilities, this class of materials seems greatly promising. Yet, the growing concern for lead toxicity in commercial semiconductor devices has entailed a thrust in the research of alternative lead-free perovskites, including their single crystalline forms. However, there is still no consolidated account of the state-of-the-art in this domain and accordingly, countless feasible systems still remain unexplored. To bridge this gap, we attempt to provide here, an up-to-date overview of lead-free perovskite single crystals with respect to their synthesis methods, structural diversity, stability, photophysical and electrical properties, and device applications. We discuss various approaches to designing, modeling, fabricating, and characterizing new single-crystal systems and conclude with some critical insights for further investigating this field of research.
CRIS-Team Scopus Importer:2021-07-16

Advances in wide bandgap SiC for optoelectronics - Ou, Haiyan; Ou, Yiyu; Argyraki, Aikaterini; Schimmel, Saskia; Kaiser, Michl; Wellmann, Peter; Linnarsson, Margareta K.; Jokubavicius, Valdas; Sun, Jianwu; Liljedahl, Rickard; Syväjärvi, Mikael (European Physical Journal B, 2014)
Silicon carbide (SiC) has played a key role in power electronics thanks to its unique physical properties like wide bandgap, high breakdown field, etc. During the past decade, SiC is also becoming more and more active in optoelectronics thanks to the progress in materials growth and nanofabrication. This paper will review the advances in fluorescent SiC for white light-emitting diodes, covering the polycrystalline doped SiC source material growth, single crystalline epitaxy growth of fluorescent SiC, and nanofabrication of SiC to enhance the extraction efficiency for fluorescent SiC based white LED
Keywords: SiC; wide bandgap; fluorescence

Aerial Photoluminescence Imaging of Photovoltaic Modules - Doll, Bernd; Wittmann, Ernst; Lüer, Larry; Hepp, Johannes; Buerhop-Lutz, Claudia; Hauch, Jens; Brabec, Christoph; Peters, Ian Marius (Physica Status Solidi-Rapid Research Letters, 2023)
On-site imaging of modules in photovoltaic (PV) systems requires contact-free techniques with high throughput and low cost for commercial relevance. Photoluminescence imaging satisfies these requirements, but it has so far not been used for aerial imaging. Such a system faces unique engineering and operating challenges, including the need to mount a light source on the drone and identifying module defects from images taken under low- and nonuniform irradiance. Herein, in-house developed photoluminescence aerial imaging (PLAI) setup is presented and it is demonstrated that it can be used to identify defects even with a difference of excitation intensity of up to 50%. The setup consists of a hexacopter aerial drone equipped with an illumination unit and a near-infrared camera. The unit is capable of partially illuminating full-sized modules at night and capturing the photoluminescence response. In the maiden flight, a throughput of 13.6 PV modules per minute is achieved, and a throughput of 300 PV modules per minute is feasible. It is shown that the setup can be used to detect and identify cracks and potential induced degradation with high levels of confidence. These findings are verified by cross correlation and comparing captured photoluminescence images to electroluminescence images taken indoors.
CRIS-Team Scopus Importer:2023-05-26
Keywords: aerial inspection; photoluminescence; photovoltaic

Aerial photoluminescence imaging of PV modules - Doll, Bernd; Wittmann, Ernst; Lüer, Larry; Buerhop-Lutz, Claudia; Hauch, Jens; Brabec, Christoph; Peters, Ian Marius (Conference Record of the IEEE Photovoltaic Specialists Conference, 2023)
On-site imaging of photovoltaic systems requires methods that are high-throughput, low-cost and contact free for commercial relevance. Photoluminescence imaging satisfies these requirements, but it has so far not been used for aerial imaging due to a lack of a drone-mounted system. In this study, we present first results captured by our in-house developed PLAI (photoluminescence aerial imaging) setup. The setup consists of a hexacopter aerial drone equipped with an illumination unit and a near infrared camera. The unit is capable of partially illuminating full size modules at night and capturing the photoluminescence response. We show that the setup can be used to detect and identify defects such as cracks and potential-induced degradation with high levels of confidence.
CRIS-Team Scopus Importer:2024-12-16

Aerosol jet printed AgNW electrode and PEDOT:PSS layers for organic light-emitting diode devices fabrication - Hamjah, Mohd Khairulamzari; Steinberger, Marc; Tam, Kai Cheong; Egelhaaf, Hans Joachim; Brabec, Christoph; Franke, Jörg (2021 14th International Congress: Molded Interconnect Devices, MID 2021 - Proceedings, 2021)
Aerosol jet printing is a cutting-edge technology offering a plethora of advantages in organic optoelectronics fabrication. In this work, we fabricated organic light-emitting diodes on glass substrates. Silver nanowires (AgNWs) and poly (3,4-ethylene dioxythiophene) polystyrene sulfonate (PEDOT:PSS) were aerosol-jet printed as the bottom electrode and hole transport layer, respectively. The other remaining layer materials were blade coated to form a multi-layered structure of the devices. The results show that the organic lightemitting diode device with 40 mm2 active areas was successfully obtained. A comparison study of blade-coated organic light-emitting diode devices on indium tin oxide based electrode is also discussed. The results of this work show that aerosol jet printing technology enables fully solution-based fabrication of organic light-emitting diode devices.
CRIS-Team Scopus Importer:2021-04-02
Keywords: 4-ethylene dioxythiophene) polystyrene sulfonate; aerosol jet printing; organic light-emitting diode; poly(3; silver nanowires

Aerosol-Jet-Printed Encapsulation of Organic Photovoltaics - Basu, Robin; Siah, Kok Siong; Distler, Andreas; Häußler, Felix; Franke, Jörg; Brabec, Christoph; Egelhaaf, Hans-Joachim (Advanced Engineering Materials, 2023)
Organic electronic devices (OEDs) are prone to oxygen- and water-induced degradation and therefore need to be encapsulated with barrier materials. In this work, an aerosol jet (AJ)-printing process is developed to coat perhydropolysilazane (PHPS) directly onto OEDs by adapting the print setup and systematically optimizing the process parameters. Furthermore, a novel curing process that converts PHPS to silica barrier layers is developed by combining damp heat (DH) exposure with subsequent vacuum–UV irradiation. This two-step treatment is shown to be considerably faster and gentler than the state-of-the-art curing processes and also yields a quantitatively higher conversion. Both the printing and the conversion process are fully compatible with OED devices, which is demonstrated by a damage-free direct encapsulation of organic solar cells. The encapsulated cells show a significant reduction of degradation in DH conditions (65 °C/85% r.h.), maintaining >95% of their initial performance for >100 h. Complementary electroluminescence measurements reveal that the AJ-printed barrier layers effectively prevent lateral water ingress into the devices. Herein, the proof of principle is provided that AJ printing can be used to print barrier layers directly onto OEDs and is thus an industrially highly relevant technology to precisely encapsulate such devices even on 3D objects.
CRIS-Team Scopus Importer:2023-07-07
Keywords: aerosol jet printing; organic solar cells; perhydropolysilazane; printed barriers; solution-processed encapsulation

Aerosol-Jet-Printed Silver Nanowires as Top Electrodes in Organic Photovoltaic Devices - Arango-Marín, Vanessa; Rocha-Ortiz, Juan S.; Osterrieder, Tobias; Barabash, Anastasia; Osvet, Andres; Wortmann, Jonas; Heumüller, Thomas; Liu, Chao; Hauch, Jens; Brabec, Christoph J. (Solar RRL, 2025)
Aerosol jet printing (AJP) is an effective method for manufacturing organic photovoltaic (OPV) devices for indoor use. Its noncontact deposition, without posttreatment, and high-resolution 3D pattern printing capabilities make it ideal for using functional nanomaterial inks. This study explores ultrasonic AJP (uAJP) atomization to deposit silver nanowires (AgNW) as the top electrode layer (TEL) in OPV devices. The OPV stack is fabricated up to the hole transport layer using high-throughput screening (HTS) methodologies. Different deposition techniques, including spin-coating, blade-coating, and uAJP of AgNW inks, as well as thermal evaporation of silver, are compared. Scanning electron microscopy analysis shows that the E2X AgNW ink formed a compact TEL layer. Combining HTS setups, right selection of interlayers and uAJP method, automated, solution-processed OPV devices with power conversion efficiencies of 9.54% on an active layer of 0.0232 cm2 are achieved, the highest reported for OPV devices using uAJP AgNW inks as top electrodes.
CRIS-Team Scopus Importer:2025-01-31
Keywords: aerosol jet printing; organic photovoltaics; ultrasonic spray coating

A facile one-step method to reduce surface impurities in solution-processed CuInS2 nanocrystal solar cells - Stahl, Melissa S.; Azimi, Seyed Hamed; Brabec, Christoph (Journal of Materials Chemistry A, 2015)
The presence of impurities and disorders presents a potential barrier for the success of solution processed inorganic nanocrystalline devices. The removal of impurities typically requires harsh conditions and complex procedures that limit utility. This paper demonstrates the successful use of a set of solvents, which can efficaciously remove the surface impurities formed during in situ deposition of CuInS2 nanocrystals. These impurities include a hard-to-remove byproduct melamine that is formed by the decomposition of thiourea at elevated temperatures, and other organic residues like amines, conjugated organic systems, as well as ketones, aldehydes or esters. This work provides some design rules for the selection of solvents for removal purposes that could potentially be used for other absorber materials as well.

A flexible nanofiber membrane containing dendritic oxygen probe for visual monitoring pressure distribution - Wang, Ting; Cai, Shaoyong; Wu, Jianchang; Jiang, Chengwei; Xiao, Ziyu; Akram, Muhammad; Cao, Ge; Tian, Yanqing (Talanta, 2024)
Pressure-sensitive paints (PSP) enable non-intrusive visualization of surface pressure distribution on model surface which is important for aerodynamic studies. However, conventional PSP materials suffer from photobleaching and inadequate sensitivity. In this work, we rationally designed and synthesized novel dendritic oxygen probes (PT1 and PT2) by covalently grafting fluorinated dendrons onto platinum tetrakis(pentafluorophenyl)porphyrin (PT0) (a common oxygen probe). Subsequently, PT2 loaded nanofibers membranes from polycaprolactone (PCL) were fabricated by electrospinning. Fabricated membranes showed high oxygen sensitivity (I0/I100 = 35.3) with excellent flexibility, good reversibility, and outstanding photostability (merely 2.0% intensity loss after prolonged irradiation). The pressure sensitivity was found around 0.73 % per kilopascal. Furthermore, significant variation in emission intensity with respect to the variation in air pressure (1.3–101.32 kPa), facilitates the naked eye visualization of the pressure distribution on the membrane surface. Such excellent oxygen and pressure sensitivity and photostability might be due to high fluorine contents of complex dendritic structure of PT2. This flexible fluorine-functionalized dendritic oxygen probe puts forward a facile and effective strategy to develop advanced PSP materials enabling accurate pressure mapping for aerodynamic studies.
CRIS-Team Scopus Importer:2024-05-10
Keywords: Dendritic copolymer; Fluorine; Oxygen sensitivity; Platinum porphyrin; Pressure-sensitive paints

Afterglow Effects as a Tool to Screen Emissive Nongeminate Charge Recombination Processes in Organic Photovoltaic Composites. - Keivanidis, Panagiotis E.; Itskos, Grigorios; Kan, Zhipeng; Aluicio-Sarduy, Eduardo; Goudarzi, Hossein; Kamm, Valentin; Laquai, Frédéric; Zhang, Weimin; Brabec, Christoph; Floudas, George; McCulloch, Iain (ACS Applied Materials and Interfaces, 2020)
Disentangling temporally overlapping charge carrier recombination events in organic bulk heterojunctions by optical spectroscopy is challenging. Here, a new methodology for employing delayed luminescence spectroscopy is presented. The proposed method is capable of distinguishing between recombination of spatially separated charge carriers and trap-assisted charge recombination simply by monitoring the delayed luminescence (afterglow) of bulk heterojunctions with a quasi time-integrated detection scheme. Applied on the model composite of the donor poly(6,12-dihydro-6,6,12,12- tetraoctyl-indeno[1,2-b]fluorene-alt-benzothiadiazole) (PIF8BT) polymer and the acceptor ethyl-propyl perylene diimide (PDI) derivative, that is, PIF8BT:PDI, the luminescence of charge-transfer (CT) states created by nongeminate charge recombination on the ns to μs timescale is observed. Fluence-dependent, quasi time-integrated detection of the CT luminescence monitors exclusively emissive charge recombination events, while rejecting the contribution of other early-time emissive processes. Trap-assisted and bimolecular charge recombination channels are identified based on their distinct dependence on fluence. The importance of the two recombination channels is correlated with the layer's order and electrical properties of the corresponding devices. Four different microstructures of the PIF8BT:PDI composite obtained by thermal annealing are investigated. Thermal annealing of PIF8BT:PDI shrinks the PDI domains in parallel with the growth of the PIF8BT domains in the blend. Common to all states studied, the delayed CT luminescence signal is dominated by trap-assisted recombination. Yet, the minor fraction of fully separated charge recombination in the overall CT emission increases as the difference in the size of the donor and acceptor domains in the PIF8BT:PDI blend becomes larger. Electric field-induced quenching measurements on complete PIF8BT:PDI devices confirm quantitatively the dominance of emissive trap-limited charge recombination and demonstrates that only 40% of the PIF8BT/PDI CT luminescence comes from the recombination of fully-separated charges, taking place within 200 ns after photoexcitation. The method is applicable to other nonfullerene acceptor blends beyond the system discussed here, if their CT state luminescence can be monitored.
Keywords: solar cell; photodetector; perylene diimides; fill factor; charge trapping; delayed luminescence; multiple-diode equivalent circuit; nonfullerene acceptors

A fulleropyrrolidine-phthalocyanine dyad for photovoltaic applications - Loi, M.A.; Denk, Patrick; Hoppe, H.; Neugebauer, H.; Meissner, Dieter; Winder, C.; Brabec, Christoph; Sariciftci, N. Serdar; Gouloumis, Andreas; Vazquez, Purificacion; Torres, Tomas (Synthetic Metals, 2003)
We report on photophysical properties of a novel dyad molecule having as antenna/donor a Zn-phthalocyanine derivative and as acceptor a C derivative covalently attached. We found evidences for long living photoinduced electron transfer in solid state. Photovoltaic action of thin film devices of the dyad is demonstrated.
Keywords: Fullerene; Photoinduced charge transfer; Phthalocyanines; Solar cells

A General Guideline for Vertically Resolved Imaging of Manufacturing Defects in Organic Tandem Solar Cells - Karl, André; Osvet, Andres; Li, Ning; Brabec, Christoph (Advanced Materials Interfaces, 2020)
Organic tandem solar cells recently made great improvements with power conversion efficiencies (PCEs) over 15%, making them attractive for further large-scale production and industrial applications. However, compared to their single-junction counterparts, the complicated device architectures of organic tandem solar cells strongly restrict their processing and upscaling to larger scales. Therefore, fast and reliable quality control measures are crucial for developing organic tandem photovoltaic technologies towards commercialization. Some of the most widely used means for quality control are luminescence imaging and lock-in thermography respectively. While effective techniques, they are limited in some respects. For example, determining the lateral position of a defect is easily possible, while the exact resolution in which layer of a thin film stack a defect is located, is challenging. This is particularly the case for tandem cells with complicated multi-layer cell architectures. This approach to overcome this challenge is the introduction of well-defined artificial defects into certain layers of an organic tandem cell stack and subsequently performing imaging analysis of the defected cells with several complementary methods. The unique response from cells with artificial defects using different imaging techniques and excitation sources can then be transferred to the imaging of devices with naturally occurring manufacturing defects.
CRIS-Team Scopus Importer:2020-05-22
Keywords: defects; imaging; organic tandem solar cells; quality control

A Generalized Crystallization Protocol for Scalable Deposition of High-Quality Perovskite Thin Films for Photovoltaic Applications - Guo, Fei; Qiu, Shudi; Hu, Jinlong; Wang, Huahua; Cai, Boyuan; Li, Jianjun; Yuan, Xiaocong; Liu, Xianhu; Forberich, Karen; Brabec, Christoph; Mai, Yaohua (Advanced Science, 2019)
Metal halide perovskite solar cells (PSCs) have raised considerable scientific interest due to their high cost-efficiency potential for photovoltaic solar energy conversion. As PSCs already are meeting the efficiency requirements for renewable power generation, more attention is given to further technological barriers as environmental stability and reliability. However, the most major obstacle limiting commercialization of PSCs is the lack of a reliable and scalable process for thin film production. Here, a generic crystallization strategy that allows the controlled growth of highly qualitative perovskite films via a one-step blade coating is reported. Through rational ink formulation in combination with a facile vacuum-assisted precrystallization strategy, it is possible to produce dense and uniform perovskite films with high crystallinity on large areas. The universal application of the method is demonstrated at the hand of three typical perovskite compositions with different band gaps. P-i-n perovskite solar cells show fill factors up to 80%, underpinning the statement of the importance of controlling crystallization dynamics. The methodology provides important progress toward the realization of cost-effective large-area perovskite solar cells for practical applications.
CRIS-Team Scopus Importer:2019-07-09
Keywords: blade coating; one-step; perovskites

A generic concept to overcome bandgap limitations for designing highly efficient multi-junction photovoltaic cells - Guo, Fei; Li, Ning; Fecher, Frank W.; Gasparini, Nicola; Ramírez Quiroz, César Omar; Bronnbauer, Carina; Hou, Yi; Radmilovic, Vuk V.; Radmilovic, Velimir R.; Spiecker, Erdmann; Forberich, Karen; Brabec, Christoph (Nature Communications, 2015)
The multi-junction concept is the most relevant approach to overcome the Shockley-Queisser limit for single-junction photovoltaic cells. The record efficiencies of several types of solar technologies are held by series-connected tandem configurations. However, the stringent current-matching criterion presents primarily a material challenge and permanently requires developing and processing novel semiconductors with desired bandgaps and thicknesses. Here we report a generic concept to alleviate this limitation. By integrating series- and parallel-interconnections into a triple-junction configuration, we find significantly relaxed material selection and current-matching constraints. To illustrate the versatile applicability of the proposed triple-junction concept, organic and organic-inorganic hybrid triple-junction solar cells are constructed by printing methods. High fill factors up to 68% without resistive losses are achieved for both organic and hybrid triple-junction devices. Series/parallel triple-junction cells with organic, as well as perovskite-based subcells may become a key technology to further advance the efficiency roadmap of the existing photovoltaic technologies.
Keywords: GEOBASE Subject Index: fuel cell; photovoltaic system; solar power EMTREE medical terms: Article; electric current; electric potential; electrical equipment; multi junction photovoltaic cell

A generic green solvent concept boosting the power conversion efficiency of all-polymer solar cells to 11% - Li, Zhenye; Ying, Lei; Zhu, Peng; Zhong, Wenkai; Li, Ning; Liu, Feng; Huang, Fei; Cao, Yong (Energy and Environmental Science, 2019)
Advances in organic photovoltaic technologies have always been closely associated with a deeper understanding of bulk-heterojunction (BHJ) microstructure morphology, which is generally governed by the ink-formulation based on a single solvent or solvent mixtures. The relatively slow progress in all-polymer solar cells (all-PSCs) is mainly due to the significant difficulty in mastering their intricate BHJ morphology dealing with entanglements of polymer chains, limiting their performance typically to 8-10%. In this work, we demonstrate that the performance of all-PSCs can be further developed to a benchmark value of 11% by manipulating the BHJ morphology using a green solvent system based on cyclopentyl methyl ether (CPME). The generic applicability of the superior ink-formulation is successfully validated in four different all-polymer solar cells, exhibiting great promise of advancing all-PSCs towards industrial production and commercialization.
CRIS-Team Scopus Importer:2019-05-28

A generic interface to reduce the efficiency-stability-cost gap of perovskite solar cells - Hou, Yi; Du, Xiaoyan; Scheiner, Simon; McMeekin, David P.; Wang, Zhiping; Li, Ning; Killian, Manuela; Chen, Haiwei; Richter, Moses; Levchuk, Ievgen; Schrenker, Nadine; Spiecker, Erdmann; et al. (Science, 2017)
A major bottleneck delaying the further commercialization of thin-film solar cells based on hybrid organohalide lead perovskites is the interface losses in state-of-the-art devices. We present a generic interface architecture that combines solution-processed, reliable, and cost-efficient hole-transporting materials, without compromising efficiency, stability or scalability of perovskite solar cells. Tantalum doped tungsten oxide (Ta-WOx)/conjugated polymer multilayers offer a surprisingly small interface barrier and form quasi-ohmic contacts universally with various scalable conjugated polymers. Using a simple regular planar architecture device, Ta-WOx doped interface-based perovskite solar cells achieve maximum efficiencies of 21.2% and combined with over 1000 hours of light stability based on a self-assembled monolayer. By eliminating additional ionic dopants, these findings open up the whole class of organics as scalable hole-transporting materials for perovskite solar cell

A generic surfactant-free approach to overcome wetting limitations and its application to improve inkjet-printed P3HT:non-fullerene acceptor PV - Maisch, Philipp; Eisenhofer, Lena M.; Tam, Kai Cheong; Distler, Andreas; Voigt, Monika M.; Brabec, Christoph; Egelhaaf, Hans-Joachim (Journal of Materials Chemistry A, 2019)
Solution based thin film technology often implies challenging wetting behaviour which has to be improved in order to achieve good printing or coating qualities. A common way of solving such problems is the use of wetting agents but they often show undesired side effects. In this work, we introduce a generic strategy to overcome this problem. We demonstrate inkjet printed arrays of poly(3,4-ethylenedioxythiophene)-polystyrene sulfonate (PEDOT:PSS) dots to efficiently pin the three-phase contact line of wet films, thereby enforcing homogenous wetting and subsequent drying on low energetic surfaces. By printing and drying single droplets of ink, a matrix of anchoring points is created which pins the subsequently printed continuous wet layer and thus enables the coating of large surface areas with homogeneous, defect free films. This method also allows convenient patterning of surfaces by combining inkjet-printing of anchoring points with subsequent large area flood coating, e.g., by doctor blading. Furthermore, the defined placement of each anchoring point allows full thermodynamic control of the film formation by quantitative calculation of the processing windows and patterning precision. The beneficial application of this new strategy to printed electronics is demonstrated by fabricating organic solar cells with power conversion efficiencies of 5%. This is achieved by printing a hydrophilic PEDOT:PSS electron blocking layer without addition of surfactants at unprecedented quality onto an otherwise non-wettable hydrophobic active layer consisting of poly(3-hexylthiophene) (P3HT) and the indacenodithiophene-based non-fullerene acceptor O-IDTBR.
CRIS-Team Scopus Importer:2019-06-18

AgIn5S8/ZnS Quantum Dots for Luminescent Down-Shifting and Anti-Reflective Layer in Enhancing Photovoltaic Performance - Kong, Mengqin; Osvet, Andres; Barabash, Anastasia; Zhang, Kaicheng; Hu, Huiying; Elia, Jack; Erban, Christof; Yokosawa, Tadahiro; Spiecker, Erdmann; Batentschuk, Miroslaw; Brabec, Christoph (ACS Applied Materials and Interfaces, 2023)

A High Throughput Platform to Minimize Voltage and Fill Factor Losses - Haffner-Schirmer, Julian; Le Corre, Vincent Marc; Forberich, Karen; Egelhaaf, Hans-Joachim; Osterrieder, Tobias; Wortmann, Jonas; Liu, Chao; Weitz, Paul; Heumüller, Thomas; Bornschlegl, Andreas; Wachsmuth, Josua; Distler, Andreas; et al. (Advanced Energy Materials, 2025)
Organic photovoltaics (OPV) now can exceed 20% power conversion efficiency in single junction solar cells. To close the remaining gap to competing technologies, both fill factor and open-circuit voltage must be optimized. The Langevin reduction factor is a well-known concept that measures the degree to which charge extraction is favored over charge recombination. It is therefore ideally suited as an optimization target in high-throughput workflows; however, its evaluation so far requires expert interaction. Here, an integrated high-throughput workflow is presented, able to obtain the Langevin reduction factor within a few seconds with high accuracy without human intervention and thus suited for autonomous experiments. This is achieved by combining evidence from UV–vis spectra, current–voltage curves, and a novel implementation of microsecond transient absorption kinetics allowing, for the first time, the intrinsic determination of charge absorption cross-sections, which is crucial to reporting stationary charge densities. The method is demonstrated by varying the donor:acceptor ratio of the high performance OPV blend PM6:Y12. The high reproducibility of the method allows to find a strictly exponential relationship between the PM6 exciton energy and the Langevin reduction factor.
CRIS-Team Scopus Importer:2025-01-31
Keywords: charge dynamics; high throughput; Langevin reduction factor; organic photovoltaics; transient absorption kinetics

A History and Perspective of Non-Fullerene Electron Acceptors for Organic Solar Cells - Armin, Ardalan; Li, Wei; Sandberg, Oskar J.; Xiao, Zuo; Ding, Liming; Nelson, Jenny; Neher, Dieter; Vandewal, Koen; Shoaee, Safa; Wang, Tao; Ade, Harald; Heumüller, Thomas; et al. (Advanced Energy Materials, 2021)
Organic solar cells are composed of electron donating and accepting organic semiconductors. Whilst a significant palette of donors has been developed over three decades, until recently only a small number of acceptors have proven capable of delivering high power conversion efficiencies. In particular the fullerenes have dominated the landscape. In this perspective, the emergence of a family of materials–the non-fullerene acceptors (NFAs) is described. These have delivered a discontinuous advance in cell efficiencies, with the significant milestone of 20% now in sight. Intensive international efforts in synthetic chemistry have established clear design rules for molecular engineering enabling an ever-expanding number of high efficiency candidates. However, these materials challenge the accepted wisdom of how organic solar cells work and force new thinking in areas such as morphology, charge generation and recombination. This perspective provides a historical context for the development of NFAs, and also addresses current thinking in these areas plus considers important manufacturability criteria. There is no doubt that the NFAs have propelled organic solar cell technology to the efficiencies necessary for a viable commercial technology–but how far can they be pushed, and will they also deliver on equally important metrics such as stability?.
CRIS-Team Scopus Importer:2021-01-22
Keywords: non-fullerene electron acceptors; organic solar cells; review and perspective

Air-processed organic tandem solar cells on glass: Toward competitive operating lifetimes - Adams, Jens; Spyropoulos, Georgios; Salvador, Michael Filipe; Li, Ning; Strohm, Sebastian; Lucera, Luca; Langner, Stefan; Machui, Florian; Zhang, Hong; Ameri, Tayebeh; Voigt, Monika M.; Krebs, Frederik C.; et al. (Energy and Environmental Science, 2015)
Photovoltaic devices based on organic semiconductors (OPVs) hold great promise as a cost-effective renewable energy platform because they can be processed from solution and deposited on flexible plastics using roll-to-roll processing. Despite important progress and reported power conversion efficiencies of more than 10% the rather limited stability of this type of devices raises concerns towards future commercialization. The tandem concept allows for both absorbing a broader range of the solar spectrum and reducing thermalization losses. We designed an organic tandem solar cell with an inverted device geometry comprising environmentally stable active and charge-selecting layers. Under continuous white light irradiation, we demonstrate an extrapolated, operating lifetime in excess of one decade. We elucidate that for the current generation of organic tandem cells one critical requirement for long operating lifetimes consists of periodic UV light treatment. These results suggest that new material approaches towards UV-resilient active and interfacial layers may enable efficient organic tandem solar cells with lifetimes competitive with traditional inorganic photovoltaics.

Air-processed polymer tandem solar cells with power conversion efficiency exceeding 10% - Li, Ning; Brabec, Christoph (Energy and Environmental Science, 2015)
The power conversion efficiencies (PCEs) of the state-of-the-art organic tandem solar cells are steadily improved in the range of 10-12%, which can be mainly attributed to the design and development of highly efficient absorbers with complementary absorption spectra. However, the impressive recorded efficiencies are only achieved for devices spin-coated in an inert atmosphere, which does not directly contribute to the commercialization of the organic photovoltaic technology. Herein, we perform a systematic study of PTB7-Th-based single-junction solar cells fabricated under various conditions. The relatively low photovoltaic performance and poor environmental stability of the air-processed devices are successfully improved by a post-treatment with alcohol-based solvents. The effect of solvent treatment is valid for both regular and inverted device architecture. Tandem devices fabricated by doctor-blading in air achieve a high PCE of 10.03% along with an unprecedentedly high FF of 76.6%.
Keywords: Engineering controlled terms: Conversion efficiency; Efficiency; Photovoltaic cells; Solar absorbers Design and Development; Efficient absorbers; Environmental stability; Organic photovoltaics; Photovoltaic performance; Polymer tandem solar cells; Power conversion efficiencies; Single junction solar cells Engineering main heading: Solar cells

aIR-PV-check: A quality inspection of PV-power plants without operation interruption - Buerhop, Claudia; Pickel, Tobias; Dalsass, Manuel; Scheuerpflug, Hans; Camus, Christian; Brabec, Christoph (43rd IEEE Photovoltaic Specialists Conference, PVSC 2016, 2016)
aIR-PV-check is a method using an unmanned aerial vehicles (UAV) with an infrared (IR)-camera for the quality inspection of PV-plants under real operating conditions. It enables the fast and 100%-control of PV-plants. Defective modules are detected by their temperature distribution. Besides the meteorological conditions, the interaction of defective modules within a string influences the module performance significantly as the measured and simulated data show. Thus, modules with extremely high temperatures are predominantly expected / detected in strings with only one single defective module. Consequently, string configurations and constellations of defective modules have to be considered for evaluating the quality of modules, strings and generator
Keywords: aerial thermography; monitoring; PV module defects; system performance

aIR-PV-check: A quality inspection of PV-power plants without operation interruption - Buerhop, Claudia; Pickel, Tobias; Dalsass, Manuel; Scheuerpflug, Hans; Camus, Christian; Brabec, Christoph; Brabec, Christoph J. (2017 IEEE 44th Photovoltaic Specialist Conference, PVSC 2017; Category numberCFP17PSC-ART; Code 136737, 2018)
AIR-PV-check is a method using an unmanned aerial vehicles (UAV) with an infrared (IR)-camera for the quality inspection of PV-plants under real operating conditions. It enables the fast and 100%-control of PV-plants. Defective modules are detected by their temperature distribution. Besides the meteorological conditions, the interaction of defective modules within a string influences the module performance significantly as the measured and simulated data show. Thus, modules with extremely high temperatures are predominantly expected / detected in strings with only one single defective module. Consequently, string configurations and constellations of defective modules have to be considered for evaluating the quality of modules, strings and generator
Keywords: Aerial thermography; Monitoring; PV module defects; System performance

Algorithmus zur IR-Panoramabilderstellung aus IR-Luftaufnahmen von PV-Freiflächenanlagen - Dalsaß, Manuel; Deitsch, Sergiu; Moerman, Daniil; Gallwitz, Florian; Brabec, Christoph (32. Symposium Photovoltaische Solarenergie, 2017)

Alkyl Chain Engineering of Solution-Processable Star-Shaped Molecules for High-Performance Organic Solar Cells - Min, Jie; Luponosov, Yuriy N.; Gerl, Andreas; Polinskaya, Marina S.; Peregudova, Svetlana M.; Dmitryakov, Petr V.; Bakirov, Artem V.; Shcherbina, Maxim A.; Chvalun, Sergei N.; Grigorian, Souren; Kaush-Busies, Nina; Ponomarenko, Sergei A.; et al. (Advanced Energy Materials, 2014)
The impact of alkyl side-chain substituents on conjugated polymers on the photovoltaic properties of bulk heterojunction (BHJ) solar cells has been studied extensively, but their impact on small molecules has not received adequate attention. To reveal the effect of side chains, a series of star-shaped molecules based on a triphenylamine (TPA) core, bithiophene, and dicyanovinyl units derivatized with various alkyl end-capping groups of methyl, ethyl, hexyl and dodecyl is synthesiyed and studied to comprehensively investigate structure-properties relationships. UV-vis absorption and cyclic voltammetry data show that variations of alkyl chain length have little infl uence on the absorption and highest occupied molecular orbital (HOMO)-lowest unoccupied molecular orbital (LUMO) levels. However, these seemingly negligible changes have a pronounced impact on the morphology of BHJ thin films as well as their charge carrier separation and transportation, which in turn influences the photovoltaic properties of these small-molecule-based BHJ devices. Solution-processed organic solar cells (OSCs) based on the small molecule with the shortest methyl end groups exhibit high short circuit current (Jsc) and fill factor (FF), with an efficiency as high as 4.76% without any post-treatments; these are among the highest reported for solution-processed OSCs based on star-shaped molecules.
Keywords: Engineering controlled terms: Charge carriers; Heterojunctions; Molecules; Solar cells; Stars Carrier separation; Highest occupied molecular orbital; Lowest unoccupied molecular orbital; Power conversion efficiencies; Side-chains; Star-shaped molecules; Structure property relationships; Structure-properties relationships Engineering main heading: Synthesis (chemical)

All inkjet-printed organic solar cells on 3D objects - Steinberger, Marc; Distler, Andreas; Hörber, Johannes; Tam, Kai Cheong; Brabec, Christoph; Egelhaaf, Hans-Joachim (Flexible and Printed Electronics, 2024)
Drop-on-demand inkjet printing is a promising and commercially relevant technology for producing organic electronic devices of arbitrary shape on a wide variety of different substrates. In this work we transfer the inkjet printing process of organic photovoltaic devices from 2D to 3D substrates, using a 5-axis robot system equipped with a multi-nozzle inkjet printing unit. We present a ready-to-use 3D printing system for industrial application, using a 5-axis motion system controlled by commercial 3D motion software, combined with a commonly used multi-nozzle inkjet print head controlled by the corresponding printing software. The very first time inkjet-printed solar cells on glass/ITO with power conversion efficiencies (PCEs) of up to 7% are realized on a 3D object with surfaces tilted by angles of up to 60° against the horizontal direction. Undesired ink flow during deposition of the inkjet-printed layers was avoided by proper ink formulation. In order to be able to print organic (opto-)electronic devices also on substrates without sputtered indium tin oxide bottom electrode, the bottom electrode was inkjet-printed from silver nanoparticle (AgNP) ink, resulting in the first all inkjet-printed (i.e. including bottom electrode) solar cell on a 3D object ever with a record PCE of 2.5%. This work paves the way for functionalizing even complex objects, such as cars, mobile phones, or ‘Internet of Things’ applications with inkjet-printed (opto-)electronic devices.
CRIS-Team Scopus Importer:2024-07-05
Keywords: 3D functionalization; 3D printing; inkjet printing; organic solar cells; silver nanoparticles

All Printed Photoanode/Photovoltaic Mini-Module for Water Splitting - Xu, Zhenhua; Chen, Lang; Brabec, Christoph; Guo, Fei (Small Methods, 2023)
Printing a large-area bismuth vanadate photoanode offers a promising approach for cost-effective photoelectrochemical (PEC) water splitting. However, the light absorption trade-off with charge transfer, as well as stability issues always lead to poor PEC efficiency. Here, the solution-processed recipe is advanced with BiI3 dopant for the printed deposition with controllable crystal growth. The resultant BiVO4 films prefer (001) orientation with nanorod feature on substrate, allowing a faster charge transfer and improved photocurrent. The BiVO4 photoanode in tandem with perovskite solar module delivers an operating photocurrent density of 5.88 mA cm−2 at zero bias in 3.11 cm2 active area under AM 1.5 G illumination, yielding a solar-to-hydrogen efficiency as high as 7.02% for unbiased water splitting. Equally important, the stability of the aged BiVO4 rods has been addressed to distinguish phase segregation at surface. The photocatalysis degradation composes of vanadium loss and Bi2O3 enriching at the surface, opening a lid on the long-term stability of BiVO4 photoanodes.
CRIS-Team Scopus Importer:2023-09-29
Keywords: BiVO; large area; tandem devices; water splitting

All sub-nanosecond laser monolithic interconnection of OPV modules - Kubis, Peter; Winter, Jan; Gavrilova, Anna; Hennel, Markus; Schlosser, Susanne; Richter, Isabel; Distler, Andreas; Heyder, Madeleine; Kery, Stefan; Lenk, Peter; Geiger, Stephan; Brabec, Christoph; et al. (Progress in Photovoltaics, 2019)
Although green femtosecond lasers provide outstanding quality and wide processing windows for monolithic interconnection of the individual cells in organic photovoltaic (OPV) modules, they are hardly used in commercial applications, due to cost reasons. In this work, a process has been developed that allows the monolithic interconnection in OPV modules with an infrared sub‐nanosecond laser exclusively, without compromising the performance of the modules. While the photoactive layer is removed easily by green femtosecond pulses without damaging the bottom electrode, this is not possible for infrared nanosecond pulses, due to their much larger optical penetration length, which significantly exceeds the thickness of the active layer and is well absorbed by the indium tin oxide (ITO) layer. This leads to damage of the ITO bottom electrode, which in turn compromises the functionality of the module. By systematically varying single‐pulse laser fluence and spatial pulse overlap, the laser parameters are optimized in such a way that the contact area between the residues of the metal oxide bottom electrode and the silver nanowire top electrode is maximized so that the electrical resistances of the contacts are sufficiently small not to affect device performance. This is demonstrated by presenting large‐area OPV modules based on the well‐characterized reference system P3HT:PCBM that show efficiencies of up to 2.4%. This achievement opens up the way towards reliable roll‐to‐roll (R2R) laser patterning processes with sub‐nanosecond lasers and thus represents a breakthrough with respect to cost‐effective R2R manufacturing of OPV modules, due to grossly reduced investment and maintenance costs for laser sources.<br
Keywords: sub-nanosecond pulses; flexible organic photovoltaic module; laser patterning

A low-bandgap semiconducting polymer for photovoltaic devices and infrared emitting diodes - Brabec, Christoph; Winder, C.; Sariciftci, Niyazi Serdar; Hummelen, J.C.; Dhanabalan, Anantharaman; van Hal, P.A.; Janssen, Rene A. J. (Advanced Functional Materials, 2002)
A novel low-bandgap conjugated polymer (PTPTB, E = ∼1.6 eV), consisting of alternating electron-rich N-dodecyl-2,5-bis(2′-thienyl)pyrrole (TPT) and electron-deficient 2,1,3-benzothiadiazole (B) units, is introduced for thin-film optoelectronic devices working in the near infrared (NIR). Bulk heterojunction photovoltaic cells from solid-state composite films of PTPTB with the soluble fullerene derivative [6,6]-phenyl C butyric acid methyl ester (PCBM) as an active layer shows promising power conversion efficiencies up to 1% under AM1.5 illumination. Furthermore, electroluminescent devices (light-emitting diodes) from thin films of pristine PTPTB show near infrared emission peaking at 800 nm with a turn on voltage below 4 V. The electroluminescence can be significantly enhanced by sensitization of this material with a wide bandgap material such as the poly(p-phenylene vinylene) derivative MDMO-PPV.

Alternating quinoxaline/oligothiophene copolymers - Synthesis and unexpected absorption properties - Tsami, Argiri; Bünnagel, Thorsten W.; Farrell, Tony; Scharber, Markus; Chalois, Stelios A.; Brabec, Christoph; Scherf, Ullrich (Journal of Materials Chemistry, 2007)
The optical and electronic properties of novel, alternating quinoxaline/oligothiophene donor-acceptor copolymers show an unexpected independence of absorption and photoluminescence, as well as of the HOMO/LUMO energy levels, on the length of the oligothiophene segments in the copolymer main chain. © The Royal Society of Chemistry.

Alternative approaches of SiC & related wide bandgap materials in light emitting & solar cell applications - Wellmann, Peter; Syväjärvi, Mikael; Ou, Haiyan (IOP Conf. Series: Materials Science and Engineering 56 (2014) 011001, 2014)

Alternative approaches of SiC & related wide bandgap materials in light emitting & solar cell applications, Proceedings of the E-MRS 2013 Spring Meeting, Symposium G - Wellmann, Peter; Syvaejaervi, Mikael; Ou, Haiyan (IOP Publishing Ltd, 2014)

Alternative device concepts for future requirements of organic photovoltaic cells - Waldauf, Christoph; Morana, Mauro; Denk, Patrick; Brabec, Christoph J.; Brabec, Christoph; Coakley, Kevin; Schilinsky, Pavel; Choulis, Stelios A. (Organic Photovoltaics VII, 2006)
The challenge to reversing the layer sequence of organic photovoltaics (OPVs) is to prepare a selective contact bottom cathode and to achieve a suitable morphology for carrier collection in the inverted structure. We report the creation of an efficient electron selective bottom contact based on a solution-processed Titania layer on top of Indium Tin Oxide. The use of o-xylene as the casting solvent creates an efficient carrier collection network with little vertical phase segregation, providing sufficient performance for both regular as well as inverted solar cells. We demonstrate inverted layer sequence OPVs with AM 1.5-calibrated power conversion efficiencies of over 3%.
Keywords: Electrode; Inverted cell; Organic; Photovoltaic; Titania

Aluminum and aluminum nitrides effect on nucleation sites in micro-alloyed steel - Abro, Shahid Hussain; Chandio, Alidad; Siddiqui, Muhammad Ali; Channa, Iftikhar Ahmed (Proceedings of the Pakistan Academy of Sciences B - Life and Environmental Sciences, 2019)
In the present research work an investigation has been taken to understand the effect of aluminum addition on nucleation sites of AlN particles. Two steel samples have been taken with and without aluminum addition. Steel A has no aluminum and steel B has some aluminum added. These samples have been solution heat treated first at 1200°C to dissolve the particles if already present in the steel matrix, and then these samples were heat treated at 710°C, 740°C, 770°C and 800°C respectively with a holding time of 10 to 60 seconds and were then quenched. These samples were then grinded and polished using metallography steps and revealed the microstructure after etching in two solutions Nital and Picric acid simultaneously. After initial interrogation by using the optical micrographs the SEM was utilized to further disclosed the nucleation morphologies. It was found that the 740°C with holding time of 15sec is the most critical stage to observe the nucleation sites. After having the SEM, it was concluded that for steel A, has the most preferable nucleation sites are ferrite and pearlite regions and surprisingly in steel B having aluminum addition the nucleation sites were interface of pro-eutectoid ferrite and pearlite. Optical, SEM and TEM characterization techniques were utilized to study the behavior and morphology.
CRIS-Team Scopus Importer:2021-04-20
Keywords: AlN (Aluminum nitride) particles; Aluminum; Austenite formation; EBSD etc; Lead bath; Nucleation

Aluminum doping of 6H-and 4H-SiC with a modified PVT growth method - Straubinger, Thomas; Bickermann, Matthias; Rasp, M.; Weingärtner, Roland; Wellmann, Peter; Winnacker, Albrecht (Materials Science Forum, 2002)
We report the development of a modified physical vapor transport (PVT) growth setup for the improved aluminum p-type doping of silicon carbide (SiC) single crystals. Usually aluminum doping of SiC is carried out by adding the dopant to the SiC powder source material. However, due to aluminum source depletion a strong exponential decrease of the dopant incorporation with increasing process time is observed. In addition, often defect generation takes place due to a high initial aluminum sublimation rate. In order to improve the aluminum supply we have installed an additional gas pipe which provides a continuous flux of aluminum atoms out of an external reservoir into the growth cell. We will discuss the influence of the additional gas flow on the thermal field and mass transport inside the growth cell. Technological steps will be pointed out which were necessary to establish crystal growth with structural properties comparable to the conventional PVT process. With the modified PVT method high quality SiC single crystals with an improved axial and lateral aluminum doping homogeneity were grown (4H-SiC: 2*10^16 cm^-3opo4*10^16 cm^-3; Dp=po10%; 6H-SiC: 8*10^16 cm^-3opo1:2 1017 cm3; Dp=po25%). Additionally the Dependence of the remaining doping variations on compensation with residual nitrogen and growth mechanisms together with measures for further improvement will be discussed.
Keywords: Aluminum Doping; Bulk Growth; Modified-PVT; Silicon Carbide (SiC)

Aluminum p-type Doping of Bulk SiC Single Crystals by Tri-Methyl-Aluminum - Hens, Philip; Künecke, Ulrike; Wellmann, Peter (Materials Science Forum, 2009)
We present p-type doping of bulk SiC crystals by the modified physical vapor transport (M-PVT) technique using TMA (Tri-Methyl-Aluminum). Using TMA as a dopant precursor allows a quite well defined crystal growth process control. The issue of improvement of conductivity (reduction of substrate resistivity) by reduction of unintentional acceptor compensation by nitrogen is addressed. It is shown that a decrease of compensation from approx. 3%...10% to approx. 0.5%...2.5% leads to a charge carrier mobility and, hence, conductivity increase of about factor tw
Keywords: Bulk Growth; M-PVT; Doping; Tri-Methyl-Aluminum

Aluminum p-type doping of silicon carbide crystals using a modified physical vapor transport growth method - Straubinger, Thomas; Bickermann, Matthias; Weingärtner, Roland; Wellmann, Peter; Winnacker, Albrecht (Journal of Crystal Growth, 2002)
We report the development of a modified physical vapor transport (PVT) growth setup for the improved aluminum p-type doping of silicon carbide (SiC) single crystals. Usually aluminum doping of SiC is carried out by adding the dopant to the SiC powder source material. However. due to aluminum source depletion a strong exponential decrease of the dopant incorporation with increasing process time is observed. In addition. often defect generation takes place due to a high initial aluminum sublimation rate. In order to improve the aluminum supply we have installed an additional gas pipe which provides a continuous flux of aluminum atoms out of an external reservoir into the growth cell. We will discuss the influence of the additional gas flow on the thermal field and mass transport inside the growth cell. Technological steps will be pointed out which were necessary to establish crystal growth with structural properties comparable to the conventional PVT process. With the modified PVT method high quality SiC single crystals with an improved axial and lateral aluminum doping homogeneity were grown (4H-SiC: 2 x 10(16) cm(-3) < p < 4 x 10(16) cm(-3) Deltap/p < 10%; 6H-SiC: 8 x 10(16) cm(-3) < p < 1.2 10(17) cm(-3). Deltap/p < 25%). (C) 2002 Elsevier Science B.V. All rights reserved.
Keywords: Doping; Growth from vapor; Semiconducting silicon compounds; modified PVT; SiC

A matter of design and coupling: high indoor charging efficiencies with organic solar modules directly coupled to a sodium ion battery - Kin, Li Chung; Distler, Andreas; Astakhov, Oleksandr; Kone, Bakary; Kungl, Hans; Karl, André; Merdzhanova, Tsvetelina; Eichel, Rüdiger A.; Brabec, Christoph; Rau, Uwe (Journal of Materials Chemistry A, 2024)
To tackle the challenge of powering distributed autonomous indoor sensors and electronics, such as in the implementation of the internet of things (IOT), a high-efficiency solar module with integrated storage is a potential solution that offers a stable, reliable power source. For this, organic photovoltaics (OPV) are a promising candidate, delivering high efficiencies under indoor lighting, flexibility, scalability and low-cost designs via roll-to-roll manufacturing. Pairing an OPV device with batteries made from widely available sodium seems to be a viable strategy for achieving a low-cost, low-power, self-charging power source. PV devices can be coupled directly to batteries without power conditioning. Self-sustained operation and stable power output of this power harvester are achievable with proper voltage matching and scaling of both the PV and battery within the target range of operating conditions. We achieved a record indoor direct charging overall efficiency of an OPV and sodium ion battery of 13.1-14.4% over a wide range of LED illumination intensities of 150-15 000 lx.
CRIS-Team Scopus Importer:2024-11-01

Ammonothermal Synthesis of Earth-Abundant Nitride Semiconductors ZnSiN2 and ZnGeN2 and Dissolution Monitoring by In Situ X-ray Imaging - Häusler, Jonas; Schimmel, Saskia; Wellmann, Peter; Schnick, Wolfgang (Chemistry - A European Journal, 2017)
In this contribution, first synthesis of semiconducting ZnSiN2 and ZnGeN2 from solution is reported with supercritical ammonia as solvent and KNH2 as ammonobasic mineralizer. The reactions were conducted in custom-built highpressure autoclaves made of nickel-based superalloy. The nitrides were characterized by powder X-ray diffraction and their crystal structures were refined by the Rietveld method. ZnSiN2 (a=5.24637(4), b=6.28025(5), c=5.02228(4) a, Z=4, Rwp=0.0556) and isotypic ZnGeN2 (a=5.46677(10), b=6.44640(12), c=5.19080(10) a, Z=4, Rwp=0.0494) crystallize in the orthorhombic space group Pna21 (no. 33). The morphology and elemental composition of the nitrides were examined by electron microscopy and energy-dispersive X-ray spectroscopy (EDX). Well-defined single crystals with a diameter up to 7 mm were grown by ammonothermal synthesis at temperatures between 870 and 1070 K and pressures up to 230 MPa. Optical properties have been analyzed with diffuse reflectance measurements. The band gaps of ZnSiN2 and ZnGeN2 were determined to be 3.7 and 3.2 eV at room temperature, respectively. In situ X-ray measurements were performed to exemplarily investigate the crystallization mechanism of ZnGeN2. Dissolution in ammonobasic supercritical ammonia between 570 and 670K was observed which is quite promising for the crystal growth of ternary nitrides under ammonothermal conditions.
Keywords: ammonothermal synthesis; in situ X-ray imaging; nitrides; semiconductor; solvothermal synthesis

A multi-objective optimization-based layer-by-layer blade-coating approach for organic solar cells: rational control of vertical stratification for high performance - Sun, Rui; Guo, Jie; Wu, Qiang; Zhang, Zhuohan; Yang, Wenyan; Guo, Jing; Shi, Mumin; Zhang, Yaohong; Kahmann, Simon; Ye, Long; Jiao, Xuechen; Loi, Maria A.; et al. (Energy and Environmental Science, 2019)
A major breakthrough in organic solar cells (OSCs) in the last thirty years was the development of the bulk heterojunction (BHJ) solution processing strategy, which effectively provided a nanoscale phase-separated morphology, aiding in the separation of Coulombically bound excitons and facilitating charge transport and extraction. Compared with the application of the layer-by-layer (LbL) approach proposed in the same period, the BHJ spin-coating technology shows overwhelming advantages for evaluating the performance of photovoltaic materials and achieving more-efficient photoelectric conversion. Thus, in this study, we have further compared the BHJ and LbL processing strategies via the doctor-blade coating technology because it is a roll-to-roll compatible high-throughput thin film fabrication route. We systematically evaluated multiple target parameters, including morphological characteristics, optical simulation, physical kinetics, device efficiency, and blend stability issues. It is worth emphasizing that our findings disprove the old stereotypes such as the BHJ processing method is superior to the LbL technology for the preparation of high-performance OSCs and the LbL approach requires an orthogonal solvent and donor/acceptor materials with special solubility. Our studies demonstrate that the LbL blade-coating approach is a promising strategy to effectively reduce the efficiency-stability gap of OSCs and even a superior alternative to the BHJ method in commercial applications.
CRIS-Team WoS Importer:2019-10-25

An adhesive bonding approach by hydrogen silsesquioxane for silicon carbide-based LED applications - Lin, Li; Ou, Yiyu; Jokubavicius, Valdas; Syväjärvi, Mikael; Liang, Meng; Liu, Zhiqiang; Yi, Xiaoyan; Schuh, Philipp; Wellmann, Peter; Herstrøm, Berit; Jensen, Flemming; Ou, Haiyan (Materials Science in Semiconductor Processing, 2019)
We report an adhesive bonding approach using hydrogen silsesquioxane (HSQ) for silicon carbide (SiC) samples. A hybrid light-emitting diode (LED) was successfully fabricated through bonding a near-ultraviolet (NUV) LED grown on a commercial 4H-SiC substrate to a free-standing boron-nitrogen co-doped fluorescent-SiC epi-layer. The bonding quality and the electrical performance of the hybrid LED device were characterized. Neither voids nor defects were observed which indicates a good bonding quality of the proposed HSQ approach. A strong warm white emission was successfully obtained from the hybrid LED through an electric current injection of 30 mA.<br
Keywords: Hydrogen silsesquioxane bonding; Fluorescent-silicon carbide; Warm white light-emitting diodes

An alcohol-dispersed conducting polymer complex for fully printable organic solar cells with improved stability - Jiang, Youyu; Dong, Xinyun; Sun, Lulu; Liu, Tiefeng; Qin, Fei; Xie, Cong; Jiang, Pei; Hu, Lu; Lu, Xin; Zhou, Xianmin; Meng, Wei; Li, Ning; et al. (Nature Energy, 2022)
Efficient and stable organic solar cells via full coating are highly desirable. Poly(3,4-ethylenedioxythiophene):polystyrene sulfonate (PEDOT:PSS) is a classic conducting polymer complex and widely used for hole collection in fully printable devices. However, PEDOT:PSS is typically dispersed in water and exhibits strong acidity that deteriorates device efficiency and stability. Here we report an alcohol-dispersed formulation (denoted as PEDOT:F) by adopting perfluorinated sulfonic acid ionomers as counterions. The ionomers have a special advantage of having two solubility parameters and can be dispersed in water or alcohols, which enables us to prepare PEDOT:F formulations dispersed in alcohols. The alcohol-dispersed formulation has good wetting properties and low acidity, which avoids the drawbacks of aqueous PEDOT:PSS. Fully printable organic photovoltaics (from bottom electrode to top electrode) based on PEDOT:F were obtained with a power conversion efficiency of 15% and could retain 83% of the initial efficiency under continuous illumination at maximum power point tracking for 1,330 h.
CRIS-Team Scopus Importer:2022-04-22

An Alternative Strategy to Adjust the Recombination Mechanism of Organic Photovoltaics by Implementing Ternary Compounds - Gasparini, Nicola; Salvador, Michael Filipe; Fladischer, Stefanie; Katsouras, Athanasios; Avgeropoulos, Apostolos; Spiecker, Erdmann; Chochos, Christos L.; Brabec, Christoph; Ameri, Tayebeh (Advanced Energy Materials, 2015)
Trap-assisted recombination is one of the main loss mechanisms in bulk-heterojunction (BHJ) solar cells. Results suggest that introducing a near infrared (NIR) polymer into the 2,3-bis(3-(octyloxy)phenyl)quinoxaline (PIDTTQ):[6,6]-phenyl C butyric acid methyl ester (PCBM) host system suppresses trap-assisted recombination in the binary blend, leading to a significant improvement of ≈60% in power conversion efficiency for ternary organic solar cells at low light intensity.
Keywords: IR sensitization; low light intensity; organic solar cells; recombination; ternary blends

Analysis of compositional gradients in Cu(In,Ga)(S,Se)2 solar cell absorbers using energy dispersive x-ray analysis with different acceleration energies - Künecke, Ulrike; Schuster, Matthias; Wellmann, Peter (Materials, 2021)
The efficiency of Cu(In,Ga)(S,Se)2 (CIGSSe) solar cell absorbers can be increased by the optimization of the Ga/In and S/Se gradients throughout the absorber. Analyzing such gradients is therefore an important method in tracking the effectiveness of process variations. To measure compositional gradients in CIGSSe, energy dispersive X-ray analysis (EDX) with different acceleration energies performed at both the front surface and the backside of delaminated absorbers was used. This procedure allows for the determination of compositional gradients at locations that are millimeters apart and distributed over the entire sample. The method is therefore representative for a large area and yields information about the lateral homogeneity in the millimeter range. The procedure is helpful if methods such as secondary ion-mass (SIMS), time-of-flight SIMS, or glow-discharge optical emission spectrometry (GDOES) are not available. Results of such EDX measurements are compared with GDOES, and they show good agreement. The procedure can also be used in a targeted manner to detect local changes of the gradients in inhomogeneities or points of interest in the m range. As an example, a comparison between the compositional gradients in the regular absorber and above the laser cut separating the Mo back contact is shown.<br
CRIS-Team Scopus Importer:2021-06-18
Keywords: Characterization; Cu(In; Ga)Se2; Energy dispersive X-ray analysis; Gradients; Solar cell; Thin films

Analysis of defects dominating carrier recombination in CeO2 single crystal for photocatalytic applications - Zhang, Endong; Brabec, Christoph; Kato, Masashi (Journal of Physics D: Applied Physics, 2024)
In photocatalytic water splitting and CO2 reduction, recently, cerium oxide (CeO2) has been widely investigated. Defects that can directly dominate carrier recombination are essential for the photocatalytic performance of CeO2. In this study, several photoluminescence (PL) peaks are observed on the (100) face of an undoped CeO2 single crystal, indicating the presence of defects. Moreover, we characterize carrier recombination using time-resolved photoluminescence (TR-PL) and microwave photoconductivity decay (μ-PCD) measurements. The temperature dependence of decay curves is the result of carrier trapping and emission at deep levels. These decay curves are observed separately using a 565 nm band-pass filter (BPF) based on the PL spectra. The trap energy level ( E T ) and majority carrier capture cross-section ( σ T ) of each defect are also analyzed using rate equations to fit the experimental results. The temperature-dependent time constants are well reproduced by a recombination model using hole traps HTinfrared and HTvisible at E T of 0.76 and 0.55 eV from the conduction or valence band, with estimated σ T of the order of 10−21 and 10−22 cm2 for without and with the BPF, respectively. These findings regarding the presence of multiple defects in a single crystal indicate the necessity to focus on defect control.
CRIS-Team Scopus Importer:2025-02-04
Keywords: carrier recombination; CeO; defect analysis; photocatalyst; single crystal

Analysis of Digitized PV-Module/System Data for Failure Diagnosis - Buerhop, Claudia; Pickel, Tobias; Teubner, Janine; Doll, Bernd; Hauch, Jens; Brabec, Christoph (36th EU PVSEC 2019 Conference, 2019)
EL-images disclose many failures in PV-modules, e. g. cell cracks. Their impact and the relevance of certain defect features on the performance during operation is not known. This study focused on the identification of defective power-relevant cells, their impact on the performance and the degradation. Therefore, pre-cracked, low-performing modules are integrated in a string and monitored on module level. As a result, a statistical analysis of EL-images identified the power-relevant cells. The power of defective modules is extremely sensitive to changing measurement conditions. Historical monitoring data and actual EL-images give evidence that so far no changes of the crack structures of fractured cells occurred. Strong seasonal impact is observed. However, the yield is rather stable during the inspection peri

Analysis of graphitization during physical vapor transport growth of silicon carbide - Wellmann, Peter; Herro, Ziad Georges; Sakwe, Aloysius; Masri, P.; Bogdanov, M.; Karpov, S.; Kulik, A.; Ramm, M.; Makarov, Y. (Materials Science Forum, 2004)
We have analyzed the graphitization process of the source material during physical vapor transport growth of SiC by comparison of experimental monitoring (digital x-ray imaging, and C-13-labeling) and 2D numerical modeling of the sublimation and recrystallization process. Growth runs under different conditions (temperature and inert gas pressure) were used for verification of the calculated source evolution. Effects like formation of a condensed disk on top of the source material, consumption of SiC powder close to the hot graphite walls, mass transport through the core part and along the side walls could be confirmed. The rate of the sublimation and recrystallization effect, however, was overestimated by the model in the range of the experimental parameters in this study. Regardless of the latter, the crystal growth rate was described very well (modeling: 280mum/h, experiment: 310mum/h and 300mum/h
Keywords: Numerical Modeling; Physical Vapor Transport; Source Material; X-Ray Imaging

Analysis of inhomogeneous local distribution of Potential induced degradation at a rooftop photovoltaic installation - Buerhop, Claudia; Pickel, Tobias; Patel, Tirth; Fecher, Frank W.; Zetzmann, Cornelia; Camus, Christian; Hauch, Jens; Brabec, Christoph (IET Renewable Power Generation, 2017)
Potential induced degradation (PID) of photovoltaic (PV) modules is one of the frequently observed failures in PV installations nowadays. This study investigates the inhomogeneous and complex PID generation on rooftop installations on industrial buildings as well as its impact on the module performance. The PID development is exemplarily presented for a 314kWp PV-plant installed in the Atlantic coastal climate. Due to the complex plant geometry and resulting irradiation situation the existence of PID could not be identified based on the annual yield data. By Infrared imaging PID was clearly identified. Evaluating historic monitoring data, the impact of PID on the string and plant performance could be quantified. A linear correlation between the defect ratio and the performance rate as well as the degradation loss rate could be formulated. © The Institution of Engineering and Technology 2017.
Keywords: Engineering controlled terms: Infrared imagingOffice buildings Compendex keywords Induced degradationIndustrial buildingsLinear correlationLocal distributionsModule performancePhotovoltaic installationPhotovoltaic modulesPlant performance Engineering main heading: Thermography (imaging)

Analysis of silicon incorporation into VGF-grown GaAs - Birkmann, Bernhard; Weingärtner, Roland; Wellmann, Peter; Wiedemann, B.; Müller, Georg (Journal of Crystal Growth, 2002)
The incorporation of silicon into VGF-grown GaAs is examined by Hall effect measurements, spark source mass spectrometry and photoluminescence (PL). It is found that the silicon is incorporated into the crystal according to Scheils-law with the Si concentration [Si] rising from 1.5 x 10(18) to 1 x 10(19) cm(-3). It is found that the intensity of the PL peak with energy close to the band gap decreases with increasing Si content of the material, whereas the intensity of the PL peak related to the acceptor SiGaVGa shows opposite behaviour. A compensation model which takes into account the acceptors Si-As and SiGaVGa is developed. The model describes the relationship between [Si] and the charge carrier concentration n up to silicon concentrations of 1 x 10(19) cm(-3) in GaAs grown under low thermal gradients. (C) 2002 Elsevier Science B.V. All rights reserved.
Keywords: Doping; Point defects; Segregation; Semiconducting gallium arsenide

Analysis of the basal plane dislocation density and thermomechanical stress during 100 mm PVT growth of 4H-SiC - Steiner, Johannes; Roder, Melissa; Nguyen, Binh Duong; Sandfeld, Stefan; Danilewsky, Andreas; Wellmann, Peter (Materials, 2019)
Basal plane dislocations (BPDs) in 4H silicon carbide (SiC) crystals grown using the physical vapor transport (PVT) method are diminishing the performance of SiC-based power electronic devices such as pn-junction diodes or MOSFETs. Therefore, understanding the generation and movement of BPDs is crucial to grow SiC suitable for device manufacturing. In this paper, the impact of the cooldown step in PVT-growth on the defect distribution is investigated utilizing two similar SiC seeds and identical growth parameters except for a cooldown duration of 40 h and 70 h, respectively. The two resulting crystals were cut into wafers, which were characterized by birefringence imaging and KOH etching. The initial defect distribution of the seed wafer was characterized by synchrotron white beam X-ray topography (SWXRT) mapping. It was found that the BPD density increases with a prolonged cooldown time. Furthermore, small angle grain boundaries based on threading edge dislocation (TED) arrays, which are normally only inherited by the seed, were also generated in the case of the crystal cooled down in 70 h. The role of temperature gradients inside the crystal during growth and post-growth concerning the generation of shear stress is discussed and supported by numerical calculations.
CRIS-Team Scopus Importer:2019-07-19
Keywords: Basal plane dislocation; Physical vapor transport; Silicon carbide; Small angle grain boundary; Thermal stress

Analysis of the Morphology of the Growth Interface as a Function of the Gas Phase Composition during the PVT Growth of Silicon Carbide - Arzig, Matthias; Künecke, Ulrike; Salamon, Michael; Uhlmann, Norman; Wellmann, Peter (Materials Science Forum, 2022)
The growth conditions of 75 mm SiC crystals in the PVT process is varied by different methods while the temperature field is kept constant. The addition of graphite into the source material leads to the formation of an ordered step flow with step heights of 0.014 µm, while the addition of graphite into the source together with N2 doping changes the step kinetics on the main facet, leading to very large, bunched steps of 0.17 µm. When elemental Si was added into the source material large macro steps are formed on the whole crystal surface. While the doping induced step bunching is related to the incorporation kinetics, the large steps induced in Si-rich conditions are attributed the reduction of surface energy. With the variation of the inert gas pressure the morphology of the surface is altered, similarly. Under low pressure conditions (0.2 mbar) a fine step structure evolves, while at a high pressure (40mbar) large surface steps are formed on the whole growth interface. Large surface steps are strongly impeded in their lateral motion at defects permeating the growth interface. At these sites the formation of foreign polytypes is facilitated.
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Keywords: 4H-SiC; bulk growth; gas phase composition; polytype switch; PVT; step bunching

Analysis on defect generation during the SiC bulk growth process - Hofmann, Heinz-Dieter; Schmitt, E.; Bickermann, Matthias; Kölbl, M.; Wellmann, Peter; Winnacker, Albrecht (Materials Science and Engineering B-Advanced Functional Solid-State Materials, 1999)
SiC crystals (1.2–1.5%% diameter) were grown by the modified Lely technique on seeds with different micropipe densities in order to study the defect generation during seeding and subsequent bulk growth. The micropipe generation is found to be strongly correlated with the occurrence of second phases in SiC like carbon inclusion formation. Model approaches for stable SiC growth conditions, i.e. without inclusions, are discussed. Numerical modeling was performed to reveal the radial and axial temperature gradients of our crucible set-up. Stress formation and micropipe generation are determined to be enhanced in the presence of a large axial temperature gradient. <br
Keywords: Physical vapor transport; SiC bulk crystal growth; Micropipe formation; Modeling of SiC sublimation growth

Analytical Model for Light Modulating Impedance Spectroscopy (LIMIS) in All-Solid-State p-n Junction Solar Cells at Open-Circuit - Almora Rodriguez, Osbel; Miravet, Daniel; Matt, Gebhard; Garcia-Belmonte, Germà; Brabec, Christoph (Applied Physics Letters, 2020)
Potentiostatic impedance spectroscopy (IS) is a well-known tool for characterization of materials and electronic devices. It can be complemented by numerical simulation strategies relying on drift-diffusion equations without any equivalent circuit-based assumptions. This implies the time-dependent solutions of the transport equations under small perturbation of the external bias applied as a boundary condition at the electrodes. However, in the case of photosensitive devices, a small light perturbation modulates the generation rate along the absorber bulk. This work then approaches a set of analytical solutions for the signals of IS and intensity modulated photocurrent and photovoltage spectroscopies, intensity modulated photocurrent spectroscopy (IMPS) and intensity modulated photovoltage spectroscopy (IMVS), respectively, from one-sided p-n junction solar cells at the open-circuit. Subsequently, a photoimpedance signal named “light intensity modulated impedance spectroscopy” (LIMIS = IMVS/IMPS) is analytically simulated, and its difference with respect to IS suggests a correlation with the surface charge carrier recombination velocity. This is an illustrative result and the starting point for future more realistic numerical simulations.<br

Analyzing the degradation of pre-damaged PV-modules - Buerhop, Claudia; Winkler, Thilo; Wirsching, Sven; Pickel, Tobias; Bemm, Andreas; Camus, Christian; Hauch, Jens; Brabec, Christoph (Proc. SPIE 10370, Reliability of Photovoltaic Cells, Modules, Components, and Systems X, 2017)
Cracked PV-modules are frequently detected in PV-systems. The impact of cracked cells on the energy yield and module performance under real operating conditions is not yet understood but of great relevance. Standard tests cannot reveal the relevant information conclusively. Therefore, we conducted a twofold analysis. 1) field exposure (global analysis on string level as well as detailed analysis on module level), and 2) load testing in the lab. Here, we present comparative electroluminescence (EL-) images recorded in an outdoor test stand and during load testing. Additionally, infrared (IR-) images as well as power data obtained from loaded and operating (field) conditions are discusse
Keywords: pre-cracked modules; field tests; loading tests; power measurements; IR-imaging; performance loss

Analyzing the efficiency, stability and cost potential for fullerene-free organic photovoltaics in one figure of merit - Li, Ning; Mcculloch, Iain; Brabec, Christoph (Energy and Environmental Science, 2018)
The power conversion efficiencies (PCEs) of solution-processed organic photovoltaic (OPV) devices continue increasing towards the 15% milestone. Recently-emerging non-fullerene acceptors (NFAs) have significantly accelerated this development. Most of the efficiency analyses performed previously are based on a fullerene acceptor without considering its contribution to the enhancement of photo-absorption and PCE. Moreover, the stability and cost potential of OPV devices are usually not discussed, which sometimes makes the efficiency prediction less representative for broad interest. In this work, we effectively combine the prediction of efficiencies with experimentally determined stability data to analyze and predict the commercial potential of a NFA-based OPV product. Assuming that NFAs dominate the blend near IR absorption, the efficiency limit of OPV devices is predicted to be close to 20% and is found to be insensitive to the donor bandgap. With the excellent photo-stability observed for state-of-the-art NFA-based OPV devices, it is suggested that the corresponding customized donors with promising processing properties, excellent environmental stability and low synthesis complexity be designed as realistic material pairs for large-scale production and commercializatio
Keywords: Engineering controlled terms: ForecastingFullerenesImage enhancementNanostructured materialsStability Engineering uncontrolled terms Commercial potentialEfficiency predictionsEnvironmental stabilityLarge scale productionsOrganic photovoltaic devicesOrganic photovoltaicsPower conversion efficienciesProcessing properties Engineering main heading: Efficiency

Analyzing the outdoor degradation behavior of organic solar modules in North China - Liu, Shaopeng; Zhang, Dawei; Egelhaaf, Hans-Joachim; Wang, Gaoyuan; Li, Xiaogang; Heumüller, Thomas; Brabec, Christoph; Li, Ning (Journal of Materials Chemistry A, 2024)
The outdoor stability of organic solar modules (OSMs) directly determines the success of the organic photovoltaic (OPV) technology, which is critically important but insufficiently studied so far. Here, we perform a systematic study on the long-term outdoor exposure of OSMs according to the ISOS-O-2 standard lasting over two years. OSMs featuring a large active area (108 cm2), lightweight design (∼22 g), and typical PCE value (4.2%) were utilized in this study. The environmental data and OSMs' property data are synchronously collected to investigate the relationship between the outdoor properties of OSMs and environmental factors with the aid of machine learning and traditional mathematical methods. Based on the experimental results, we quantify the OSMs' degradation process and evaluate the long-term stability of OSMs. Encouragingly, we find that the long-term operational stability of OSMs is quite impressive under the outdoor aging conditions in North China. The initial outdoor PCE value was around 4%, maintaining over 3.3% even after two years of outdoor exposure. The extrapolated degradation rate remained below 2% per year, despite the burn-in process. The observed burn-in process during outdoor degradation suggests that mitigating burn-in loss could enhance the field stability of OSMs, and that the outdoor environment can be effectively simulated in a well-designed laboratory setting for stability studies. All of this suggests a bright future for further development of OPV technology towards commercialization and practical outdoor applications.
CRIS-Team Scopus Importer:2024-05-31

An Automated Workflow to Discover the Structure-Stability Relations for Radiation Hard Molecular Semiconductors - Bornschlegl, Andreas; Duchstein, Patrick; Wu, Jianchang; Rocha-Ortiz, Juan S.; Caicedo-Reina, Mauricio; Ortiz, Alejandro; Insuasty, Braulio; Zahn, Dirk; Lüer, Larry; Brabec, Christoph (Journal of the American Chemical Society, 2025)
Emerging photovoltaics for outer space applications are one of the many examples where radiation hard molecular semiconductors are essential. However, due to a lack of general design principles, their resilience against extra-terrestrial high-energy radiation can currently not be predicted. In this work, the discovery of radiation hard materials is accelerated by combining the strengths of high-throughput, lab automation and machine learning. This way, a large material library of more than 130 organic hole transport materials is automatically processed, degraded, and measured. The materials are degraded under ultraviolet-C (UVC) light in a nitrogen atmosphere, serving as the conditions for electromagnetic radiation hardness tests. A value closely related to the differential quantum yield for photodegradation is extracted from the evolution of the UV-visible (UV-vis) spectra over time and used as a stability target. Following this procedure, a stability ranking spanning over 3 orders of magnitude was obtained. Combining Gaussian Process Regression based on predictors from structural fingerprints and manual filtering of the materials by features, structure-stability relations for UVC stable materials could be found: Fused aromatic ring clusters are beneficial, whereas thiophene, methoxy and vinylene groups are detrimental. Comparing the UV-vis spectra of the degraded material in film and solution, bond cleavage could be made out as the leading degradation mechanism. Even though UVC light can in principle break most organic bonds, the stable materials are able to distribute and dissipate the energy well enough so that the chemical structures remain stable. The established predictive model quantifies the effect of specific molecular features on UVC stability, allowing chemists to consider UVC stability in their molecular design strategy. In the future, a larger data set will allow to inversely design molecular semiconductors which show high performance and radiation hardness at the same time.
CRIS-Team Scopus Importer:2025-01-31

An efficient solution-processed intermediate layer for facilitating fabrication of organic multi-junction solar cells - Li, Ning; Baran, Derya; Forberich, Karen; Turbiez, Mathieu; Ameri, Tayebeh; Krebs, Frederik C.; Brabec, Christoph (Advanced Energy Materials, 2013)
Photovoltaic tandem technology has the potential to boost the power conversion efficiency of organic photovoltaic devices. Here, a reliable and efficient fully solution-processed intermediate layer (IML) consisting of ZnO and neutralized poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) is demonstrated for series-connected multi-junction organic solar cells (OSCs). Drying at 80°C in air is sufficient for this solution-processed IML to obtain excellent functionality and reliability, which allow the use of most of high performance donor materials in the tandem structure. An open circuit voltage (V) of 0.56 V is obtained for single-junction OSCs based on a low band-gap polymer, while multi-junction OSCs based on the same absorber material deliver promising fill factor values along with fully additive V as the number of junctions increase. Optical and electrical simulations, which are reliable and promising guidelines for the design and investigation of multi-junction OSCs, are discussed. The outcome of optical and electrical simulations is in excellent agreement with the experimental data, indicating the outstanding efficiency and functionality of this solution-processed IML. The demonstration of this efficient, solution-processed IML represents a convenient way for facilitating fabrication of multi-junction OSCs to achieve high power conversion efficiency. An efficient solution-processed intermediate layer is introduced for facilitating fabrication of multi-junction organic solar cells (OSCs). The multi-junction OSCs that incorporate this intermediate layer deliver promising fill factor values along with the fully additive open circuit voltage (V) as the number of junctions increase. © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
Keywords: electrical simulation; low temperature treatment; optical stimulation; organic tandem solar cells; solution-processed intermediate layers; ZnO-nanoparticles

A New Crystal Phase Molybdate Yb2Mo4O15: The Synthesis and Upconversion Properties - Wang, Hai-Qiao; Mackovic, Mirza; Osvet, Andres; Litzov, Ivan; Epelbaum, Elena; Stiegelschmitt, Alfons; Batentschuk, Miroslaw; Spiecker, Erdmann; Brabec, Christoph (Particle & Particle Systems Characterization, 2015)
A new upconversion nanocrystal phase Yb2Mo4O15:Er is developed by using a facile aqueous-precipitation procedure combined with thermal annealing. Nanocrystals of Yb2Mo4O15 are exclusively synthesized, with particle sizes ranging from 1 to 20 nm. The optical properties are characterized and a high upconversion quantum yield is determined to be approximate to 1.3% at room temperature, under excitation of approximate to 500 mW cm(-2) IR (975 nm). To the best of our knowledge, this is the first work concerning the synthesis of nanocrystalline Yb2Mo4O15 and the characterization of its upconversion properties, which possesses the potential to be utilized in bio-probing and thin-film optoelectronic device applications.
Keywords: upconversion; Yb2Mo4O15:Er; nanocrystals; characterization

A new dithienosilole-based oligothiophene with methyldicyanovinyl groups for high performance solution-processed organic solar cells - Luponosov, Yuriy N.; Min, Jie; Ameri, Tayebeh; Brabec, Christoph; Ponomarenko, Sergei A. (Organic Electronics, 2014)
A new linear dithienosilole-based oligothiophene end-capped with methyl and electron-withdrawing dicyanovinyl groups, DTS(Oct)-(2T-DCV-Me), was prepared in good yield. This oligomer exhibited broad absorption spectra in bulk down to the near-IR region with the optical edge at 900 nm, resulting in an initially high power conversion efficiency of 5.44% in solution-processed organic solar cells using PCBM as an acceptor.
Keywords: Dicyanovinyl groups; Donor-acceptor oligomer; Oligothiophene; Organic solar cell; Small molecule

A New Metric for Assessing Local Mechanical Load Scenarios for PV Modules at Specific Locations - Camus, Christian; Offermann, Pascal; Weissmann, Martin; Buerhop-Lutz, Claudia; Hauch, Jens; Brabec, Christoph (33rd EUPVSEC, 2017)
In this paper, a new metric for assessing the location-specific mechanical loads imposed by snow or wind gusts which a photovoltaic module can be expected to be exposed to at a given location is introduced. For demonstrating this general approach, two locations of moderate distance ( 110km) in Northern Bavaria are compared. It is shown that even on moderate distances the expected loads differ by a factor of four or more highlighting the importance of location-specific requirements for PV modules. For assessing the loads, the historical weather data of the closest surrounding weather station is evaluated in order to deduce an expectation value for the site of interest. This data is analyzed with respect to the frequency and severity of the relevant weather events such that the annuality of a weather event of a given severity can be determined. Finally, the severity of an event corresponding to a single occurrence in 20 years, i.e. a standard product warranty, is chosen to represent the requirements of a location with respect to a certain parameter.
Keywords: Photovoltaic; Forecast; Reliability; Weather

A new two-dimensional oligothiophene end-capped with alkyl cyanoacetate groups for highly efficient solution-processed organic solar cells - Cui, Chaohua; Min, Jie; Ho, Cheuk-Lam; Ameri, Tayebeh; Yang, Pei; Zhao, Jianzhang; Brabec, Christoph; Wong, Wai-Yeung (Chemical Communications, 2013)
A new two-dimensional small molecule (DCA3T(VT)BDT) with an acceptor-donor-acceptor framework showed a high power conversion efficiency of 4% with a high fill factor of up to 0.63 in solution-processed organic solar cells. © 2013 The Royal Society of Chemistry.
Keywords: EMTREE drug terms: alkyl cyanoacetate; alkyl group; oligothiophene; thiophene derivative; unclassified drug EMTREE medical terms: article; electric potential; energy resource; organic solar cell; synthesis

Angle dependence of external and internal quantum efficiencies in bulk-heterojunction organic solar cells - Dennler, Gilles; Forberich, Karen; Scharber, Markus; Brabec, Christoph; Tomis, Igor; Hingerl, Kurt; Fromherz, Thomas (Journal of Applied Physics, 2007)
The realization of highly efficient organic solar cells requires the understanding and the optimization of the light path in the photoactive layer. We present in this article our approach to measure and model the optical properties of our bulk-heterojunction devices, and to control them in order to enhance the photovoltaic performances. We report our recent observations on the dependence of the external quantum efficiency (EQE) on the incidence angle of the light, and our results on the determination of internal quantum efficiency based on EQE measurement and optical modeling cross-checked by reflection measurements. We investigate poly(3-hexylthiophene): 1-(3-methoxy-carbonyl) propyl-1- phenyl [6,6] C61 based solar cells with two different thicknesses of the active layer (170 and 880 nm), and show that in the thin ones the absorption is enhanced for oblique incident radiation. © 2007 American Institute of Physics.

An improved algorithm for calculating relaxation time spectra from material functions of polymers with monodisperse and bimodal molar mass distributions - Brabec, Christoph; Schausberger, Alois (Rheologica Acta, 1995)
Using the basic concept of Emri and Tschoegl, the algorithm for calculating relaxation time spectra has been improved such that excellent results are provided in the difficult case of polymers with narrow molar mass distributions. These spectra can be compared with those calculated by nonlinear regularization (Weese 1992), which we regard as a very exact method, and show equally good results with even less mathematical effort. Examples of dense relaxation time spectra (up to eight points per decade) are given for nearly monodisperse polystyrene melts and for mixtures of these up to four components. The relaxation time spectra describe the dynamic mechanical experimental data in each case with an overall error of less than 3%. The filtering method used to avoid physically senseless oscillations has been proven to resolve the characteristic peaks contributed by monodisperse polymers accurately. © 1995 Steinkopff Verlag.
Keywords: dynamic moduli; iterative filtering method; molar mass distribution; Relaxation time spectra

An Innovative Anode Interface Combination for Perovskite Solar Cells with Improved Efficiency, Stability, and Reproducibility - Meng, Wei; Xu, Junyi; Dong, Lirong; Zhang, Jiyun; Xie, Zhiqiang; Luo, Junsheng; Zhao, Baolin; Zhang, Kaicheng; Osvet, Andres; Heumüller, Thomas; Forberich, Karen; Halik, Marcus; et al. (Solar RRL, 2022)
Rational design and engineering of top interface layers with combined properties of effective passivation, high thermal- and photo-stability are effective methods to advance the commercialization of perovskite photovoltaics. Here, an innovative anode interface combination is developed based on alcohol-dispersed poly (3-hexylthiophene-2,5-diyl) (P3HT) nanoparticles as the hole transport material and chlorobenzene-dissolved trioctylphosphine oxide (TO PO) as the passivation agent. It is shown that instead of the commonly used 2D passivation ligands, TOPO-passivated perovskite films exhibit greatly improved thermal stability. Furthermore, the passivation contributes to an enhanced carrier lifetime and reduced surface trap density, yielding an improvement in the quasi-fermi-level splitting of 57 meV. To maintain surface passivation during solution processing of further layers, it is necessary to develop a hole transport layer that can be processed from orthogonal solvents. P3HT nanoparticles formulated in alcoholic media fully meet this requirement, clearly benefitting from their high vertical conductivity and extremely low contact resistance with carbon electrodes. Based on this configuration, device efficiency of up to 18.4% is demonstrated for perovskite solar cells with fully solution-processed carbon electrodes, along with significantly improved device stability and reproducibility.
CRIS-Team WoS Importer:2022-06-17

An insight into the temperature dependence of photoluminescence of a highly-emissive Cs-Ag(Na)Bi(In)Cl-6 perovskite - Stroyuk, Oleksandr; Raievska, Oleksandra; Osvet, Andres; Hauch, Jens; Brabec, Christoph (Journal of Materials Chemistry C, 2023)
The temperature-dependent evolution of the photoluminescence (PL) properties of a highly emissive Cs2Ag0.35Na0.65Bi0.02In0.98Cl6 perovskite was examined in the range of 80-340 K. The PL maximum exhibited a shift to higher energies with an increase in T, while the bandgap decreased with elevated T. This behavior can be explained by a thermal distribution of the self-trapped exciton states.
CRIS-Team WoS Importer:2023-03-17

An inter-laboratory stability study of roll-to-roll coated flexible polymer solar modules - Gevorgyan, Suren A.; Medford, Andrew J.; Bundgaard, Eva; Sapkota, Subarna B.; Schleiermacher, Hans-Frieder; Zimmermann, Birger; Wuerfel, Uli; Chafiq, Amine; Lira-Cantu, Monica; Swonke, Thomas; Wagner, Michael; Haillant, Olivier O.; et al. (Solar Energy Materials and Solar Cells, 2011)
A large number of flexible polymer solar modules comprising 16 serially connected individual cells was prepared at the experimental workshop at Risø DTU. The photoactive layer was prepared from several varieties of P3HT (Merck, Plextronics, BASF and Risø DTU) and two varieties of ZnO (nanoparticulate, thin film) were employed as electron transport layers. The devices were all tested at Risø DTU and the functional devices were subjected to an inter-laboratory study involving the performance and the stability of modules over time in the dark, under light soaking and outdoor conditions. 24 laboratories from 10 countries and across four different continents were involved in the studies. The reported results allowed for analysis of the variability between different groups in performing lifetime studies as well as performing a comparison of different testing procedures. These studies constitute the first steps toward establishing standard procedures for an OPV lifetime characterization. © 2011 Elsevier B.V. All rights reserve
Keywords: Flexible modules; Inter-laboratory study; Outdoor testing; Polymer solar cells; R2R manufactured OPV; Round robin

Annealing-induced changes in the nature of point defects in sublimation-grown cubic silicon carbide - Schöler, Michael; Brecht, Clemens; Wellmann, Peter (Materials, 2019)
In recent years, cubic silicon carbide (3C-SiC) has gained increasing interest as semiconductor material for energy saving and optoelectronic applications, such as intermediate-band solar cells, photoelectrochemical water splitting, and quantum key distribution, just to name a few. All these applications critically depend on further understanding of defect behavior at the atomic level and the possibility to actively control distinct defects. In this work, dopants as well as intrinsic defects were introduced into the 3C-SiC material in situ during sublimation growth. A series of isochronal temperature treatments were performed in order to investigate the temperature-dependent annealing behavior of point defects. The material was analyzed by temperature-dependent photoluminescence (PL) measurements. In our study, we found a variation in the overall PL intensity which can be considered as an indication of annealing-induced changes in structure, composition or concentration of point defects. Moreover, a number of dopant-related as well as intrinsic defects were identified. Among these defects, there were strong indications for the presence of the negatively charged nitrogen vacancy complex (NC-VSi)-, which is considered a promising candidate for spin qubits.
CRIS-Team Scopus Importer:2019-08-23
Keywords: 3C-SiC; Defect engineering; Doping; Photoluminescence; Point defects; Sublimation growth

Anodic Formation of Thick Anatase TiO2 Mesosponge Layers for High-Efficiency Photocatalysis - Lee, Kiyoung; Kim, Dam-Hee; Roy, Poulomi; Paramasivam, Indhumati; Birajdar, Balaji; Spiecker, Erdmann; Schmuki, Patrik (Journal of the American Chemical Society, 2010)
We report a process for the flabrication of an anatase TiO2 mesosponge (TMS) layer by an optimized Ti anodization process in a hot glycerol electrolyte followed by a suitable etching process. Such layers can easily be grown to > 10 mu m thickness and have regular channels and structural features in the 5-20 nm range. The layers show high photocatalytic activity and are mechanically very robust. The layers therefore open new pathways to the wide field of TiO2(anatase) applications.

Anomalous charge carrier transport phenomena in highly aluminum doped SiC - Müller, Ralf; Künecke, Ulrike; Weingärtner, Roland; Maier, M.; Wellmann, Peter (Physica Status Solidi C: Conferences, 2006)
Temperature dependant Hall effect measurements were performed on aluminum doped SiC samples with specific resistivities between 8 Omega cm and 0.1 Omega cm. In all samples indications for impurity conduction at low temperatures were found. In low doped samples, a sharp transition between the impurity conduction transport regime and the hole conduction regime is visible in the temperature dependence of specific resistivity, charge carrier concentration and mobility. In highly doped samples (rho < 0.2 Omega cm), this transition is no longer confined to a small temperature range and much less abrupt. We conclude that the impurity conduction is still present at high temperatures in highly aluminum doped SiC so that at least two competing transport mechanisms are present simultaneously in these samples. (c) 2006 WILEY-VCH Verlag GmbH & Co KGaA, Weinhei
Keywords: Silicon Carbide; charge carrier transport; highly Al-doped; Hall effect

Anomaly detection in IR images of PV modules using supervised contrastive learning - Bommes, Lukas; Hoffmann, Mathis; Buerhop-Lutz, Claudia; Pickel, Tobias; Hauch, Jens; Brabec, Christoph; Maier, Andreas; Peters, Ian Marius (Progress in Photovoltaics, 2022)
Increasing deployment of photovoltaic (PV) plants requires methods for automatic detection of faulty PV modules in modalities, such as infrared (IR) images. Recently, deep learning has become popular for this. However, related works typically sample train and test data from the same distribution ignoring the presence of domain shift between data of different PV plants. Instead, we frame fault detection as more realistic unsupervised domain adaptation problem where we train on labeled data of one source PV plant and make predictions on another target plant. We train a ResNet-34 convolutional neural network with a supervised contrastive loss, on top of which we employ a k-nearest neighbor classifier to detect anomalies. Our method achieves a satisfactory area under the receiver operating characteristic (AUROC) of 73.3% to 96.6% on nine combinations of four source and target datasets with 2.92 million IR images of which 8.5% are anomalous. It even outperforms a binary cross-entropy classifier in some cases. With a fixed decision threshold, this results in 79.4% and 77.1% correctly classified normal and anomalous images, respectively. Most misclassified anomalies are of low severity, such as hot diodes and small hot spots. Our method is insensitive to hyperparameter settings, converges quickly, and reliably detects unknown types of anomalies making it well suited for practice. Possible uses are in automatic PV plant inspection systems or to streamline manual labeling of IR datasets by filtering out normal images. Furthermore, our work serves the community with a more realistic view on PV module fault detection using unsupervised domain adaptation to develop more performant methods with favorable generalization capabilities.
CRIS-Team WoS Importer:2022-04-08

An Operando Study on the Photostability of Nonfullerene Organic Solar Cells - Xiao, Jingyang; Ren, Minrun; Zhang, Guichuan; Wang, Jianbin; Zhang, Donglian; Liu, Linlin; Li, Ning; Brabec, Christoph; Yip, Hin-Lap; Cao, Yong (Solar RRL, 2019)
Nonfullerene organic solar cells (OSCs) have achieved an impressive power conversion efficiency (PCE) over the past few years, showing a great potential for real applications. However, the study on the photostability and degradation mechanism of nonfullerene OSCs is far behind than that of fullerene-based solar cells, which is crucial for the commercial applications of the technology. Herein, an efficient and stable nonfullerene OSC based on PCE10:rhodanine-benzothiadiazole-coupled indacenodithiophene with branched 2-ethylhexyl side chains (EH-IDT) is fabricated from environmentally benign solvent. The PCE10:EH-IDT solar cell shows a high PCE of 9.17% and a long operational lifetime (T-80) of 2132 h, compared with other two OSCs based on 3,9-bis(2-methylene-(3-(1,1-dicyanomethylene)-indanone)-5,5,11,11-tetrakis(4-hexylphenyl)-dithieno[2,3-d:2',3'-d']-s-indaceno[1,2-b:5,6-b']-dithiophene (ITIC) and another fuse ring acceptor with withdrawing units of 1,1-dicyanomethylene-3-indanone and hexyl side chains (IDIC) nonfullerene acceptors, with tested lifetimes of only 221 and 558 h, respectively. As indicated by the Flory-Huggins interaction parameters, ITIC and IDIC have poor miscibility with PCE10, which leads to morphology degradation, suppressed charge generation, increased trap states, and charge recombination in the photoaging test, which accounts for the significant loss of short-circuit current density and fill factor during operation. The improved miscibility of the donor and the acceptor results in a more stable morphology, and the PCE10:EH-IDT solar cells thus achieve an outstanding overall performance that combines high efficiency and superior photostability and paves the way for the potential practical applications of OSCs.
CRIS-Team WoS Importer:2019-07-26
Keywords: miscibility; nonfullerene organic solar cells; operational lifetime; photostability

A paradigmatic change: Linking fullerenes to electron acceptors - Feng, Lai; Rudolf, Marc; Wolfrum, Silke; Troeger, Anna; Slanina, Zdenek; Akasaka, Takeshi; Nagase, Shigeru; Martin, Nazario; Ameri, Tayebeh; Brabec, Christoph; Guldi, Dirk Michael (Journal of the American Chemical Society, 2012)
The potential of Lu N@C and its analogues as electron acceptors in the areas of photovoltaics and artificial photosynthesis is tremendous. To this date, their electron-donating properties have never been explored, despite the facile oxidations that they reveal when compared to those of C . Herein, we report on the synthesis and physicochemical studies of a covalently linked Lu N@C -perylenebisimide (PDI) conjugate, in which PDI acts as the light harvester and the electron acceptor. Most important is the unambiguous evidence-in terms of spectroscopy and kinetics-that corroborates a photoinduced electron transfer evolving from the ground state of Lu N@C to the singlet excited state of PDI. In stark contrast, the photoreactivity of a C -PDI conjugate is exclusively governed by a cascade of energy-transfer processes. Also, the electron-donating property of the Lu N@C moiety was confirmed through constructing and testing a bilayer heterojunction solar cell device with a PDI and Lu N@C derivative as electron acceptor and electron donor, respectively. In particular, a positive photovoltage of 0.46 V and a negative short circuit current density of 0.38 mA are observed with PDI/Ca as anode and ITO/Lu N@C as cathode. Although the devices were not optimized, the sign of the V and the flow direction of J clearly underline the unique oxidative role of Lu N@C within electron donor-acceptor conjugates toward the construction of novel optoelectronic devices. © 2012 American Chemical Society.

A perspective on the bright future of metal halide perovskites for X-ray detection - Sytnyk, Mykhailo; Deumel, Sarah; Tedde, Sandro Francesco; Matt, Gebhard; Heiß, Wolfgang (Applied Physics Letters, 2019)
Metal halide perovskites (MHPs) changed the world of solution processed semiconductors, previously dominated by organic semiconductors, toward predominantly inorganic materials with a relatively high electron/hole mobility. A series of devices benefit from their optoelectronic properties, including X-ray detectors. After the introduction of MHP X-ray detectors in 2013, they have achieved significant improvements in the form of single crystals, polycrystalline materials, and pixelated imaging devices. In addition, MHPs in the form of colloidal nanocrystals act as excellent scintillators. We see the bright future of MHPs in energy resolved X-ray detection, either achieved in the single counting mode, or in nanocrystal multilayer stacked devices, acting as a combination of selective X-ray filters and scintillators.
CRIS-Team Scopus Importer:2019-11-15

A phase-field model for the evaporation of thin film mixtures - Ronsin, Olivier; Jang, Dongju; Egelhaaf, Hans-Joachim; Brabec, Christoph; Harting, Jens (Physical Chemistry Chemical Physics, 2020)

A polymer bilayer hole transporting layer architecture for high-efficiency and stable organic solar cells - Xu, Junyi; Heumüller, Thomas; Le Corre, Vincent Marc; Barabash, Anastasia; Félix, Roberto; Frisch, Johannes; Bär, Marcus; Brabec, Christoph (Joule, 2024)
All-solution-processed organic photovoltaic (OPV) cells allow cost- and energy-effective fabrication methods for large-area devices. Despite significant progress on laboratory-scale devices, there is still a lack of interface materials that can be solution processed on top of the active layer, are compatible with novel non-fullerene acceptors (NFAs), and also provide sufficient long-term stability. We developed a novel interface layer concept, where alcohol-based organic polymer nanoparticles can be processed on top of a polymer-NFA active layer and doped to achieve a quasi-Ohmic hole contact. Moreover, poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) is processed as a second layer, forming a bilayer solution-processed hole transporting layer (HTL), providing an industrially relevant inverted architecture with a protective PEDOT:PSS layer on top. Most importantly, exceptional stability is observed. PM6:Y6 devices with the bilayer HTL are demonstrated to maintain 93% of their initial efficiency for 1,800 h under continuous solar cell operation at 60°C.
CRIS-Team Scopus Importer:2024-10-11
Keywords: hole transport layer; nanoparticles; organic solar cell; solution-processed

Applicability of a Flat-Bed Birefringence Setup for the Determination of Threading Dislocations of Silicon Carbide Wafers - Steiner, Johannes; Nguyen, B. D.; Roder, M.; Danilewsky, A.; Sandfeld, S.; Wellmann, Peter (Materials Science Forum, 2022)
Screw-type dislocations like micropipes (MP) and threading screw dislocations (TSD) are prohibiting the function or at least diminishing the efficiency of electronic devices based on silicon carbide (SiC). Therefore, it is essential to characterize wafers in an efficient and fast manner. Molten potassium hydroxide (KOH) etching or white-beam X-ray topography (SWXRT) are either destructive in the case of KOH etching or not economically viable in the case of SWXRT for an in-depth characterization of every wafer of one SiC crystal. Birefringence microscopy is being utilized as a fast and non-destructive characterization method. Instead of microscopic setups, commercially available flat-bed scanners equipped with crossed polarizer foils can be used for fast large-area scans. This work investigates the feasibility of such a setup regarding the detection rate of MPs and TSDs. The results of a full-wafer mapping are compared with birefringence microscopy and KOH etching. In the investigated sample clusters of MPs caused by a polytype switch in the beginning of the growth could be identified by both birefringence microscopy and the flat-bed scanner setup, as well as small angle grain boundaries and threading edge dislocation (TED) arrays. However, the resolution of the scanner was not sufficient to identify TSDs. Nevertheless the setup proves to be an easy-to-setup and cheap characterization method, able to quickly identify defect clusters in 4H-SiC wafers.
Created from Fastlane, Scopus look-up
Keywords: birefringence; KOH etching; physical vapor transport; silicon carbide

Application of 3-D X-ray computed tomography for the in-situ visualization of the SiC crystal growth interface during PVT bulk growth - Neubauer, Georg; Salamon, Michael; Roider, Florian; Uhlmann, Norman; Wellmann, Peter (Materials Science Forum, 2013)
In this paper, we present for the first time an in-situ 3-D reconstruction of the SiC crystal growth interface using X-ray computed tomography (CT). We show that the shape of the growth interface can be determined with high precision at growth temperatures above 2100 °C in a conventional 3 PVT (physical vapor transport) growth system. © (2013) Trans Tech Publications, Switzerlan
Keywords: 3-D X-ray; Computed tomography; CT; PVT; SiC bulk crystal growth

Application of in-situ 3D computed tomography during PVT growth of 4H-SiC for the study of source material consumption under varying growth conditions - Wellmann, Peter; Fahlbusch, Lars; Salamon, Michael; Uhlmann, Norman (Materials Science Forum, 2016)
2D and 3D in-situ X-ray visualization was applied to study the behavior of the SiC source material during PVT growth under various growth conditions. Experiments were carried out in two growth chambers for the growth of 3 inch and 4 inch crystals. Growth parameters were varied in the gas room in terms of axial temperature and inert gas pressure. The study addresses the stability of the SiC source material surface. It is shown that a higher inert gas pressure (e.g. 25 mbar) inhibits an unintentional upward evolution of the SiC feedstock that interferes with the crystal growth interface. The latter is related to a suppression of a pronounced recrystallization inside the SiC source. For a low inert gas pressure (e.g. 10 mbar) it is concluded that the axial temperature gradient inside the source material needs to be decreased to less than ca. 10 K/c
Keywords: 3D computed tomography; In-situ x-ray visualization; SiC bulk growth

Application of optical absorbance for the investigation of electronic and structural properties of sol-gel processed TiO2 films - Welte, Andrea; Waldauf, Christoph; Brabec, Christoph J.; Wellmann, Peter (Thin Solid Films, 2008)
In this paper we report on optical absorbance as characterization technique to determine the electronic nature and, to a certain extend, also the structural properties of sol-gel deposited thin films in the 10 nm to 100 nm thickness range. In particular we have addressed the band structure of the TiO2 layers using band edge optical absorbance measurements; the crystallographic structure (i.e. amorphous, anatase, rutile, and brookite) after heat treatment in wet atmosphere was verified using X-ray diffraction (XRD) and Raman spectroscopy. In the case of structural properties we found that - after heat treatment at 200 degrees C - amorphous structural properties dominate while at higher temperatures (e.g. 500 degrees C) the anatase polytype is dominant. While XRD and Raman spectroscopy fail for 10 nm thin layers, optical absorbance proved to be a valid tool. The latter being of particular interest for the function of TiOx layers in electronic devices like sensors and solar cells. The aim of the paper is to discuss appropriate optical characterization tools for thin sol-gel processed TiO2 films. (c) 2007 Elsevier B.V. All rights reserve
Keywords: TiO2; Absorbance; Raman spectroscopy; XRD

Application of Printable ITO/PEDOT Nanocomposites as Transparent Electrodes in Optoelectronic Devices - Maksimenko, Ilja; Kilian, Daniel; Mehringer, Christian; Voigt, Michael; Peukert, Wolfgang; Wellmann, Peter (Conference on Lasers and Electro-Optics, 2012)
Printable transparent hybrid composites consisting of indium tin oxide (ITO) nanoparticles and conducting polymer 3,4-polyethylenedioxythiophene: polystyrene sulfonic acid (PEDOT:PSS)) as matrix material were developed and used as transparent electrodes in all-printed flexible electroluminescent lamps and electrochromic display
Keywords: optical devices; electro-optical devices; thin films; transparent conductive coatings

A pressure process for efficient and stable perovskite solar cells - Luo, Junsheng; Xia, Jianxing; Yang, Hua; Sun, Chunlin; Li, Ning; Malik, Haseeb Ashraf; Shu, Hongyu; Wan, Zhongquan; Zhang, Haoli; Brabec, Christoph; Jia, Chunyang (Nano Energy, 2020)
The grain boundaries of organic-inorganic halide perovskite films not only function as defect centers, but also behave as intrinsic ion migrating channels and extrinsic moisture-induced degradation initiators, which are detrimental to the efficiency and stability of perovskite solar cells (PSCs). Here, an effective methodology for fabrication of high-quality perovskite layers with reduced non-radiative recombination, suppressed ion migration and increased moisture stability is reported for the first time, referred as the pressure-assisted solution processing (PASP). Through PASP strategy, the nucleation and growth of perovskite crystals can be controlled, leading to the micron-sized grains and microsecond-range carrier lifetimes. The resultant PSC shows champion power conversion efficiency (PCE) as high as 20.74% and a stabilized efficiency exceeding 20%, with superior long-term stability, maintaining above 90% of initial PCE even aging 60 days and continuous 1-sun illumination for 200 h in ambient environment without encapsulation. We unambiguously believe that the control of perovskite crystal nucleation and growth with high quality will be an important direction to improve the efficiency of PSCs to the theoretical limit, as well as to stabilize perovskite-based materials and devices.
CRIS-Team Scopus Importer:2020-07-24
Keywords: High-efficiency; Micron-sized grains; Microsecond-range carrier lifetimes; Perovskite solar cells; Pressure; Stability

A review of the biological response to ionic dissolution products from bioactive glasses and glass-ceramics - Hoppe, Alexander; Güldal, Nusret Sena; Boccaccini, Aldo R. (Biomaterials, 2011)
Several inorganic materials such as special compositions of silicate glasses, glass-ceramics and calcium phosphates have been shown to be bioactive and resorbable and to exhibit appropriate mechanical properties which make them suitable for bone tissue engineering applications. However, the exact mechanism of interaction between the ionic dissolution products of such inorganic materials and human cells are not fully understood, which has prompted considerable research work in the biomaterials community during the last decade. This review comprehensively covers literature reports which have investigated specifically the effect of dissolution products of silicate bioactive glasses and glass-ceramics in relation to osteogenesis and angiogenesis. Particularly, recent advances made in fabricating dense biomaterials and scaffolds doped with trace elements (e.g. Zn, Sr, Mg, and Cu) and investigations on the effect of these elements on the scaffold biological performance are summarized and discussed in detail. Clearly, the biological response to artificial materials depends on many parameters such as chemical composition, topography, porosity and grain size. This review, however, focuses only on the ion release kinetics of the materials and the specific effect of the released ionic dissolution products on human cell behaviour, providing also a scope for future investigations and identifying specific research needs to advance the field. The biological performance of pure and doped silicate glasses, phosphate based glasses with novel specific compositions as well as several other silicate based compounds are discussed in detail. Cells investigated in the reviewed articles include human osteoblastic and osteoclastic cells as well as endothelial cells and stem cells. © 2011 Elsevier Ltd.
UnivIS-Import:2015-03-09:Pub.2011.tech.IW.LM.arevie
Keywords: Bioactive glasses; Bioactivity; Bone tissue engineering; Cell proliferation; Metal ion release; Osteoblasts

A review on organic nanoparticle-based optoelectronic devices: from synthesis to applications - Liu, Zhe; Xie, Chen; Heumüller, Thomas; McCulloch, Iain; Brabec, Christoph; Huang, Fei; Cao, Yong; Li, Ning (Energy and Environmental Science, 2024)
Over the past few decades, organic optoelectronic devices have shown broad application prospects. However, the solubility of organic materials requires the use of toxic solvents, hindering the fabrication of these devices in an air environment. Furthermore, the common approaches such as exploring non-halogenated solvents and side-chain modification do not address the root of this problem. In this case, considering the increasing focus on the subject of nanoparticles, dispersing organic materials as nanoparticles in non-toxic water/alcohol solvents provides a perfect and universally applicable solution to address the toxicity problem. In addition, the unique properties of nanoparticles can provide new ideas for the optimization and tuning of organic optoelectronic devices. In this review, we present an up-to-date overview of the water/alcohol-based organic nanoparticles applied in optoelectronic devices, encompassing the entire journey from nanoparticles to practical applications, which is partitioned into four vital segments: nanoparticle intrinsic property, from organic semiconducting materials to nanoparticles, organic thin films, and finally device applications.
CRIS-Team Scopus Importer:2025-02-04

A Series of Pyrene-Substituted Silicon Phthalocyanines as Near-IR Sensitizers in Organic Ternary Solar Cells - Ke, Lili; Min, Jie; Adam, Matthias; Gasparini, Nicola; Hou, Yi; Perea, Jose Dario; Chen, Wei; Zhang, Hong; Fladischer, Stefanie; Sale, Anna Chiara; Spiecker, Erdmann; Tykwinski, Rik; et al. (Advanced Energy Materials, 2016)
An attractive method to broaden the absorption bandwidth of polymer/fullerene-based bulk heterojunction (BHJ) solar cells is to blend near infrared (near-IR) sensitizers into the host system. Axial substitution of silicon phthalocyanines (Pcs) opens a possibility to modify the chemical, thermodynamic, electronic, and optical properties. Different axial substitutions are already designed to modify the thermodynamic properties of Pcs, but the impact of extending the π-conjugation of the axial ligand on the opto-electronic properties, as a function of the length of the alkyl spacer, has not been investigated yet. For this purpose, a novel series of pyrene-substituted silicon phthalocyanines (SiPc-Pys) with varying lengths of alkyl chain tethers are synthesized. The UV-vis and external quantum efficiency (EQE) results exhibit an efficient near IR sensitization up to 800 nm, clearly establishing the impact of the pyrene substitution. This yields an increase of over 20% in the short circuit current density (J ) and over 50% in the power conversion efficiency (PCE) for the dye-sensitized ternary device. Charge generation, transport properties, and microstructure are studied using different advanced technologies. Remarkably, these results provide guidance for the diverse and judicious selection of dye sensitizers to overcome the absorption limitation and achieve high efficiency ternary solar cells.
Keywords: Absorption limitations; Charge transport; Near-IR sensitizers; Silicon phthalocyanine; Ternary solar cells

A Shape-Induced Orientation Phase within 3D Nanocrystal Solids - Burian, Max; Karner, Carina; Yarema, Maksym; Heiß, Wolfgang; Amenitsch, Heinz; Dellago, Christoph; Lechner, Rainer T. (Advanced Materials, 2018)
When nanocrystals self assemble into ordered superstructures they form functional solids that may inherit the electronical properties of the single nanocrystals. To what extent these properties are enhanced depends on the positional and orientational order of the nanocrystals within the superstructure. Here, the formation of micrometer-sized free-standing supercrystals of faceted 20 nm Bi nanocrystals is investigated. The self-assembly process, induced by nonsolvent into solvent diffusion, is probed in situ by synchrotron X-ray scattering. The diffusion-gradient is identified as the critical parameter for controlling the supercrystal-structure as well as the alignment of the supercrystals with respect to the substrate. Monte Carlo simulations confirm the positional order of the nanocrystals within these superstructures and reveal a unique orientation phase: the nanocrystal shape, determined by the atomic Bi crystal structure, induces a total of 6 global orientations based on facet-to-facet alignment. This parallel alignment of facets is a prerequisite for optimized electronic and optical properties within designed nanocrystal solids. © 2018 The Authors. Published by WILEY-VCH Verlag GmbH & Co. KGaA, Weinhe
Keywords: colloidal nanocrystals; in situ SAXS; supercrystal; MC-simulation; self-assembly

A Soluble Donor-Acceptor Double-Cable Polymer: Polythiophene with Pendant Fullerenes - Cravino, Antonio; Zerza, Gerald; Maggini, Michele; Bucella, Stefania; Svensson, Mattias; Andersson, Mats R.; Neugebauer, Helmut; Brabec, Christoph; Sariciftci, Niyazi Serdar (Monatshefte für Chemie, 2003)
We report the synthesis and the spectroscopic properties of a novel soluble thiophene-based copolymer carrying pendant fullerene moieties (donor-acceptor double-cable polymer). Photoinduced absorption (PIA) experiments on spin cast films reveal a photoinduced electron transfer from the polythiophene chain onto the fullerene moieties. The performance of photovoltaic devices produced with this copolymer is also discussed.
Keywords: Double-cable polymers; Fullerenes; Organic photovoltaics; Photoinduced spectroscopy; Polythiophenes

A solution-processable star-shaped molecule for high-performance organic solar cells via alkyl chain engineering and solvent additive - Min, Jie; Luponosov, Yuriy N.; Ameri, Tayebeh; Elschner, Andreas; Peregudova, Svetlana M.; Baran, Derya; Heumüller, Thomas; Li, Ning; Machui, Florian; Ponomarenko, Sergei; Brabec, Christoph (Organic Electronics, 2013)
A new star-shaped D-π-A molecule, tris4-[5′′-(1,1- dicyanobut-1-en-2-yl)-2,2′-bithiophen-5-yl]phenylamine N(Ph-2T-DCN-Et), with high efficiency potential for photovoltaic applications was synthesized. As compared to its analogue S(TPA-bT-DCN), it showed stronger absorption in the region of 350-450 nm and a lower lying highest occupied molecular energy level (HOMO). Solution-processed organic solar cells (OSCs) based on a blend of N(Ph-2T-DCN-Et) and PCBM resulted in a high PCE of 3.1% without any post-treatment. The PCE of N(Ph-2T-DCN-Et) based solar cells was further improved to 3.6% under simulated AM 1.5 by addition of a new additive 4-bromoanisole (BrAni). © 2012 Elsevier B.V. All rights reserved.
Keywords: 4-Bromoanisole (BrAni); D-π-A molecule; Highest occupied molecular energy level; Organic solar cells (OSCs)

A solution-processed barium hydroxide modified aluminum doped zinc oxide layer for highly efficient inverted organic solar cells - Zhang, Hong; Stubhan, Tobias; Li, Ning; Turbiez, Mathieu; Matt, Gebhard; Ameri, Tayebeh; Brabec, Christoph (Journal of Materials Chemistry A, 2014)
Inverted organic solar cells (iOSCs) with air stable interface materials and top electrodes and an efficiency of 6.01% are achieved by inserting a barium hydroxide (Ba(OH)) layer between the aluminum doped zinc oxide (AZO) electron extraction layer and the active layer. A low bandgap diketopyrrolopyrrole-quinquethiophene alternating copolymer (pDPP5T-2) and phenyl-C61-butyric acid methyl ester (PCBM) were chosen as the active layer compounds. Compared to the control device without Ba(OH), insertion of a few nm thick Ba(OH) layer results in an enhanced V of 10%, J of 28%, FF of 28% and PCE of 80%. Modification of AZO with a solution processed low-cost Ba(OH) layer increased the efficiency of the inverted device by dominantly reducing the energy barrier for electron extraction from PCBM, and consequently, reduced charge recombination is observed. The drastic improvement in device efficiency and the simplicity of fabrication by solution processing suggest Ba(OH) as a promising and practical route to reduce interface induced recombination losses at the cathode of organic solar cells.
Keywords: Aluminum doped zinc oxide layers; Barium hydroxide; Inverted organic solar cells; Solution-processed

Assembling Mesoscale-Structured Organic Interfaces in Perovskite Photovoltaics - Hou, Yi; Xie, Chen; Radmilovic, Vuk V.; Puscher, Bianka; Wu, Mingjian; Heumüller, Thomas; Karl, André; Li, Ning; Tang, Xiaofeng; Meng, Wei; Chen, Shi; Osvet, Andres; et al. (Advanced Materials, 2019)
Mesoscale-structured materials offer broad opportunities in extremely diverse applications owing to their high surface areas, tunable surface energy, and large pore volume. These benefits may improve the performance of materials in terms of carrier density, charge transport, and stability. Although metal oxides–based mesoscale-structured materials, such as TiO2, predominantly hold the record efficiency in perovskite solar cells, high temperatures (above 400 °C) and limited materials choices still challenge the community. A novel route to fabricate organic-based mesoscale-structured interfaces (OMI) for perovskite solar cells using a low-temperature and green solvent–based process is presented here. The efficient infiltration of organic porous structures based on crystalline nanoparticles allows engineering efficient “n-i-p” and “p-i-n” perovskite solar cells with enhanced thermal stability, good performance, and excellent lateral homogeneity. The results show that this method is universal for multiple organic electronic materials, which opens the door to transform a wide variety of organic-based semiconductors into scalable n- or p-type porous interfaces for diverse advanced applications.<br

Assessing Temperature Dependence of Drift Mobility in Methylammonium Lead Iodide Perovskite Single Crystals - Shrestha, Shreetu; Matt, Gebhard; Osvet, Andres; Niesner, Daniel; Hock, Rainer; Brabec, Christoph (Journal of Physical Chemistry C, 2018)
Hybrid organic-inorganic perovskites have emerged as cost-effective and high-performance semiconductors for optoelectronic applications. Precise knowledge of charge carrier mobility and especially the temperature dependence of mobility is therefore of utmost relevance for advancing high-performance materials. Here, the charge carrier mobility in methylammonium lead iodide single crystals is investigated with time of flight technique from 290 to 100 K. A nondispersive transport with an electron mobility of 135 (+/- 20) cm(2)/V s and a hole mobility of 90 (+/- 20) cm(2)/V s is obtained at room temperature. A power-law temperature dependence of mobility, mu alpha T-m, with an exponent m = -2.8 and -2.0, is measured for electrons and holes in the tetragonal phase. The highest electron and hole mobilities measured are 635 (+/- 70) and 415 (+/- 20) cm(2)/V s, respectively. Our results indicate that the scattering of charge carriers with phonons is the limiting factor for carrier mobilities at room temperature.

Assessing the accuracy of imaging techniques for defect characterization on thin film solar cells - Vetter, Andreas; Hofbeck, Bernhard; Kubis, Peter; Brabec, Christoph (42nd IEEE Photovoltaic Specialist Conference, PVSC 2015, 2015)
Imaging methods are an essential tool for improving processing of solar cells. Unfortunately, it is difficult to validate the imaging methods in detail. One focus of our work was to establish an approach by which one can assess the accuracy of the determination of the influence of defects via imaging on CIGS solar cells. The method is, however, not restricted to CIGS and should be easily transferable to other solar cell types, in particular other thin film technologies. The benefit of such a method is the possibility to validate and optimize imaging techniques and, in turn, improving tools to optimize solar cell material and processing of solar cells.
Keywords: accuracy; CIGS; defects; ILIT; imaging; performance loss; quality control

Assessment of Technology- and Weather-Specific Temperature Losses of Various Photovoltaic Technologies - Brabec, Christoph (35th European Photovoltaic Solar Energy Conference and Exhibition, 2018)
In this paper, the temperature-induced performance losses of eight different photovoltaic (PV) module technologies under various real weather conditions are analyzed. Therefore, the electrical performance data of one year gathered at the ZAE Bayern’s PV test plant in Arzberg, Germany was correlated to on-site weather data and module temperature measurements. By classifying the measurement days into distinct weather categories an in-depth analysis of the weather- and technology-dependent performance is realized in this study. For each weather category, the different PV technologies are ranked with respect to their electrical yield. Subsequently, the temperature behavior of the technologies is analyzed for each of the categories in order to investigate, in how far the temperature-related yield losses are responsible for the weather-dependent performance differences that are observed for the different technologies. This analysis shows that the performance behavior is one of the main causes for the performance differences that are observed. However, it also becomes clear that further losses due to differences in spectral and / or angular sensitivity or weak light performance also influence the performance significantly. In the future, the results of this study will support system designers in choosing the appropriate PV technology for a given site based on the local climate conditio
Keywords: PV Technologies; Outdoor Performance; Yield Analysis; Temperature Behavior

A Stage-Gate Framework for Upscaling of Single-Junction Perovskite Photovoltaics - Forberich, Karen; Albrecht, Steve; Castriotta, Luigi Angelo; Distler, Andreas; Hauch, Jens; Kirchartz, Thomas; Paetzold, Ulrich W.; Schorr, Susan; Sprau, Christian; Stannowski, Bernd; Ternes, Simon; Unger, Eva; et al. (Advanced Energy Materials, 2025)
To address the challenge of upscaling single-junction perovskite photovoltaics (PV) toward market-relevant performance in a structured and efficient manner, a stage-gate approach that divides the process into stages according to technology readiness levels (TRLs) is proposed. Whereas the first stage contains only material research, the later stages are concerned with the development from lab-scale devices to large-area modules, and properties such as device size as well as processing methods are adapted step-by-step toward commercializable techniques. The stages are connected by gates that specify the criteria that must be met for a material or process to be transferred to the next stage. In addition, a literature survey for the keywords “perovskite” and “module” is performed. This analysis shows that most of the reported modules have an area between 10 cm2 and 20 cm2, corresponding to stage 3 or TRL 5 in the scheme, and operational stability is often incompletely reported. These findings analysis indicate a significant gap in the research focus on large-area modules and elevated stress and field tests, which are essential for transitioning to commercial applications. It is suggested to use the proposed stage-gate process as an efficient and structured guideline toward commercializing perovskite PV.
CRIS-Team Scopus Importer:2025-02-04
Keywords: commercialization; large-area; module; perovskites; upscaling

A star-shaped D-π-A small molecule based on a tris(2-methoxyphenyl)amine core for highly efficient solution-processed organic solar cells - Min, Jie; Luponosov, Yuriy N.; Solodukhin, Alexander N.; Kausch-Busies, Nina; Ponomarenko, Sergei A.; Ameri, Tayebeh; Brabec, Christoph (Journal of Materials Chemistry C, 2014)
A new star-shaped D-π-A small molecule, 2,2′,2′- nitrilotris[(3-methoxy-4,1-phenylene)-2,2′-bithiene-5′, 5-diyleth-1-yl-1-ylidene]trimalononitrile N(Ph(OMe)-2T-DCN-Me), with high efficiency potential for photovoltaic applications was synthesized. Introducing a soluble tris(2-methoxyphenyl)amine (TPA-MeO) core unit can significantly improve the solubility of star-shaped small molecules without negatively impacting intramolecular conjugation and intermolecular solid state arrangements. Solution-processed organic solar cells based on a blend of N(Ph(OMe)-2T-DCN-Me) and PCBM show an initially high power conversion efficiency of over 4% under simulated AM 1.5. © the Partner Organisations 201
Keywords: Engineering controlled terms: Molecules; Stars; Synthesis (chemical) High power conversion; Organic solar cell; Photovoltaic applications; Small molecules; Solution-processed; Star-shaped Engineering main heading: Solar cells

A top-down strategy identifying molecular phase stabilizers to overcome microstructure instabilities in organic solar cells - Zhang, Chaohong; Heumüller, Thomas; Leon, Salvador; Gruber, Wolfgang; Burlafinger, Klaus; Tang, Xiaofeng; Perea, Jose Dario; Wabra, Isabell; Hirsch, Andreas; Unruh, Tobias; Li, Ning; Brabec, Christoph (Energy and Environmental Science, 2019)
The operational stability of organic solar cells (OSCs) is the essential barrier to commercialization. Compared to thermally-induced degradation, photo-stability of OSCs is far away from being resolved. Here, we demonstrate that the thermal- and photo-degradation of metastable bulk-heterojunction OSCs are governed by the same mechanism. Understanding the fundamental principles behind this mechanism is of significant importance to fully address the instability issues. Structural incompatibilities between the donor and acceptor molecules are identified as the main origin of the instability. Further, we introduce a top-down approach mainly based on their melting temperature and interaction parameters to rationally screen molecular phase stabilizers from a database with more than 10000 small molecules. Eventually, five chemicals were selected to validate our concept and tested in unstable organic solar cells. 1,4-Piperazine, which possesses a high melting point, good miscibility with polymers and the capability of forming inter-molecular hydrogen bonding, can indeed stabilize the mixed amorphous phases, leading to significantly improved stability of otherwise metastable OSCs.<br

A two-scale method for the computation of solid-liquid phase transitions with dendritic microstructure - Eck, Christof; Knabner, Peter; Korotov, Sergey (Journal of Computational Physics, 2002)
A two-scale model for liquid-solid phase transitions with equiaxed dendritic microstructure in binary material in the case of slow solute diffusion is presented. The model consists of a macroscopic energy transport equation and, for each point of the macroscopic domain, a local cell problem describing the evolution of the microstructure and the microsegregation. It is derived by formal homogenization of a sharp interface model, including the Gibbs-Thomson law and kinetic undercooling. Based on the two-scale model, a numerical two-scale method for the simulation of phase transitions with dendritic microstructure is developed, and numerical examples are presented. © 2002 Elsevier Science (USA
Keywords: Crystal growth; Gibbs-Thomson law; Homogenization; Kinetic undercooling; Multiscale model; Stefan problem

A Universal Fluorinated Polymer Acceptor Enables All-Polymer Solar Cells with >15% Efficiency - Peng, Feng; An, Kang; Zhong, Wenkai; Li, Zhenye; Ying, Lei; Li, Ning; Huang, Zhenqiang; Zhu, Chunguang; Fan, Baobing; Huang, Fei; Cao, Yong (ACS Energy Letters, 2020)
While great progress has been achieved in all-polymer solar cells (all-PSCs), the efficiency of all-PSCs is primarily limited by polymer acceptors that lack a high extinction coefficient, high electron mobility, and good compatibility with polymer donors. Here we designed and developed a polymer acceptor PFA1 based on a non-fullerene acceptor framework with a fluorine substituent on the 1,1-dicyanomethylene-3-indanone unit. In combination with an electron-donating polymer, PTzBI-oF, the blend film presents an extended and intensified absorption profile, enhanced electron mobility, and favorable film morphology. The optimized all-PSCs exhibit a remarkably high efficiency of 15.11%, which is, to the best of our knowledge, the highest performance yet reported for an all-PSC. Of particular importance is the applicability of PFA1 as a universal polymer acceptor with a range of polymer donors to achieve impressively high efficiencies. These properties enable a new molecular design strategy for the construction of polymer acceptors toward applications in high-performance all-PSCs.
CRIS-Team Scopus Importer:2020-12-04

A universal interface layer based on an amine-functionalized fullerene derivative with dual functionality for efficient solution processed organic and perovskite solar cells - Azimi, Seyed Hamed; Ameri, Tayebeh; Ameri, Tayebeh; Zhang, Hong; Hou, Yi; Ramírez Quiroz, César Omar; Min, Jie; Hu, Mengyao; Zhang, Zhi-Guo; Przybilla, Thomas; Matt, Gebhard; Spiecker, Erdmann; et al. (Advanced Energy Materials, 2015)
The successful application of an effective dipolar interface layer based on an amine functionalized fullerene derivative (DMAPA-C60) is reported for the perovskite and organic photovoltaic devices. The incorporation of DMAPA-C60 facilitates a favorable energy level alignment, and results in enhanced mobility-lifetime (μt) produc
Keywords: energy level alignment; mobility-lifetime products; organic photovoltaic devices; perovskite solar cells

A universal method to form the equivalent ohmic contact for efficient solution-processed organic tandem solar cells - Li, Ning; Stubhan, Tobias; Krantz, Johannes; Machui, Florian; Turbiez, Mathieu; Ameri, Tayebeh; Brabec, Christoph (Journal of Materials Chemistry A, 2014)
The highly transparent, conductive and robust intermediate layer (IML) is the primary challenge for constructing efficient organic tandem solar cells. In this work, we demonstrate an easy but generic approach to realize the fully functional, solution-processed IMLs. In detail, solution-processed silver-nanowires are packed at low concentration between hole- and electron-transporting layers to convert an otherwise rectifying interface into an ohmic interface. The IMLs are proven to be of ohmic nature under applied bias, despite the unipolar charge selectivity of the single layers. Ohmic recombination within IMLs is further proven in organic tandem solar cells fabricated by doctor-blading under ambient conditions. The tandem solar cells based on PCDTBT:[70]PCBM as the bottom cell and pDPP5T-2:[60]PCBM as the top cell give a power conversion efficiency of 7.25%, which is among the highest values for solution-processed organic tandem solar cells fabricated by using a roll-to-roll compatible deposition method in air. © the Partner Organisations 2014.
Keywords: Engineering controlled terms: Hole concentration; Nanowires; Ohmic contacts Ambient conditions; Deposition methods; Electron-transporting layers; Intermediate layers; Low concentrations; Power conversion efficiencies; Solution-processed; Tandem solar cells Engineering main heading: Solar cells

Author Correction: Traps and transport resistance are the next frontiers for stable non-fullerene acceptor solar cells (Nature Communications, (2022), 13, 1, (3786), 10.1038/s41467-022-31326-z) - Wöpke, Christopher; Göhler, Clemens; Saladina, Maria; Du, Xiaoyan; Nian, Li; Greve, Christopher; Zhu, Chenhui; Yallum, Kaila M.; Hofstetter, Yvonne J.; Becker-Koch, David; Li, Ning; Heumüller, Thomas; et al. (Nature Communications, 2022)
The original version of this Article contained an error in Fig. 2, in which three data sets (represented by circles, squares and triangles, respectively)were shifted along the x-axis by one data point, leadin g to an incorrect representation of the “Exp. suns-Voc” data (the symbols) in Fig. 2a and 2b. The correct version of Fig. 2 is:(Figure Presented.).This has been corrected in both the PDF andHTMLversions of the Article.
CRIS-Team Scopus Importer:2022-08-12

Automated analysis of X-ray topography of 4H-SiC wafers: Image analysis, numerical computations, and artificial intelligence approaches for locating and characterizing screw dislocations - Nguyen, Binh Duong; Roder, Melissa; Danilewsky, Andreas; Steiner, Johannes; Wellmann, Peter; Sandfeld, Stefan (Journal of Materials Research, 2023)
The physical vapor transport (PVT) crystal growth process of 4H-SiC wafers is typically accompanied by the occurrence of a large variety of defect types such as screw or edge dislocations, and basal plane dislocations. In particular, screw dislocations may have a strong negative influence on the performance of electronic devices due to the large, distorted or even hollow core of such dislocations. Therefore, analyzing and understanding these types of defects is crucial also for the production of high-quality semiconductor materials. This work uses automated image analysis to provide dislocation information for computing the stresses and strain energy of the wafer. Together with using a genetic algorithm this allows us to predict the dislocation positions, the Burgers vector magnitudes, and the most likely configuration of Burgers vector signs for the dislocations in the wafer.
CRIS-Team WoS Importer:2023-02-03

Automated Synthesis of 1-Tetradecylphosphonic Acid-Capped FAPbBr3 Nanocrystals for Light Conversion in Display Applications - Hu, Huiying; Shi, Hongyang; Zhang, Jiyun; Hauch, Jens; Osvet, Andres; Brabec, Christoph (ACS Applied Nano Materials, 2024)
Perovskite nanocrystals (NCs) have garnered increasing attention as light-emitting materials owing to their high photoluminescence quantum yields (PLQY) and narrow full width at half-maximum (fwhm). However, the poor stability hinders their practical application in displays. In this work, we investigate the photostability of FAPbBr3 NCs with the modification of 1-tetradecylphosphonic acid (TDPA). Employing a high-throughput approach, the optimized FAPbBr3/TDPA NCs reached a sufficiently high PLQY of 76% with a narrow band emission of 20 nm, as opposed to 45% PLQY for FAPbBr3/oleic acid NCs. Due to the strong passivation of TDPA on the perovskite surface, NC-filled polymeric binder layers exhibit excellent photostability under environmental conditions. The optimal samples maintained 95% of the initial PL intensity after continuous intense irradiation.
CRIS-Team Scopus Importer:2024-04-26
Keywords: ligand; light conversion; perovskite nanocrystal; PLQY; stability

Automated synthesis of quantum dot nanocrystals by hot injection: Mixing induced self-focusing - Salaheldin, Ahmed M.; Walter, Johannes; Herre, Patrick; Levchuk, Ievgen; Jabbari, Yasaman; Kolle, Joel; Brabec, Christoph; Peukert, Wolfgang; Segets, Doris (Chemical Engineering Journal, 2017)
The hot injection technique for the synthesis of quantum dots (QDs) is a well-established and widely used method in the lab. However, scale-up rules do not exist. One reason is that in particular the role of process parameters like mixing on particle formation is largely unknown, as systematic examination of the latter is impossible for the laborious and complex manual synthesis. Herein we studied the mixing induced self-focusing of particle size distributions (PSDs) of CdSe QDs using automation in combination with a defined stirrer geometry. Basis for our study is a platform that allows parallelization with inline temperature monitoring, defined injection rate, accurate sampling times as well as controlled stirring. Reproducibility in terms of optical product properties was analyzed by absorption and emission whereas reproducibility in terms of the PSD was verified by deconvolution of UV/Vis absorbance spectra and especially by analytical ultracentrifugation (AUC) complemented by transmission electron microscopy (TEM). In line with previous results, AUC confirmed that even QDs made by hot injection in an automated setup are polydisperse with multimodal size distributions. Finally, reproducibility in combination with early stage sampling and controlled mixing allowed us for the first time to analyze the influence of stirring on focusing and defocusing of PSDs, that has been expressed in terms of the evolution of the relative standard deviation (RSD). Our work paves the way to gain in-depth understanding of often forgotten process-structure relationships of colloidal nanoparticles which eventually is a first step in the direction of the development of scalable synthesis and reliable application of high-quality QDs in technical application

Automatic Detection and Analysis of Photovoltaic Modules in Aerial Infrared Imagery - Dotenco, Sergiu; Dalsaß, Manuel; Winkler, Ludwig; Wurzner, Tobias; Brabec, Christoph; Maier, Andreas; Gallwitz, Florian (IEEE Winter Conference on Applications of Computer Vision, 2016)
Drone-based aerial thermography has become a convenient quality assessment tool for the precise localization of defective modules and cells in large photovoltaic-power plants. However, manual evaluation of aerial infrared recordings can be extremely time-consuming. Therefore, we propose an approach for automatic detection and analysis of photovoltaic modules in aerial infrared images. Significant temperature abnormalities such as hot spots and hot areas can be identified using our processing pipeline. To identify such defects, we first detect the individual modules in infrared images, and then use statistical tests to detect the defective modules. A quantitative evaluation of the detection and analysis pipeline on real-world, infrared recordings shows the applicability of our approac

Automatized analysis of IR-images of photovoltaic modules and its use for quality control of solar cells - Hepp, Johannes; Machui, Florian; Egelhaaf, Hans-J.; Brabec, Christoph; Vetter, Andreas (Energy Science and Engineering, 2016)
It is well known that the performance of solar cells may significantly suffer from local electric defects. Accordingly, infrared thermography (i.p. lock-in thermography) has been intensely applied to identify such defects as hot spots. As an imaging method, this is a fast way of module characterization. However, imaging leads to a huge amount of data, which needs to be investigated. An automatized image analysis would be a very beneficial tool but has not been suggested so far for lock-in thermography images. In this manuscript, we describe such an automatized analysis of solar cells. We first established a robust algorithm for segmentation (or recognition) for both, the PV-module and the defects (hot spots). With this information, we then calculated a parameter from the IR-images, which could be well correlated with the maximal power (Pmpp) of the modules. The proposed automatized method serves as a very useful foundation for faster and more thorough analyses of IR-images and stimulates the further development of quality control on solar modules. © 2016 The Authors. Energy Science & Engineering published by the Society of Chemical Industry and John Wiley & Sons Ltd.
Keywords: Imaging; IR-thermography; PV; quality control; segmentation; solar cell

Automatized segmentation of photovoltaic modules in IR-images with extreme noise - Vetter, Andreas; Hepp, Johannes; Brabec, Christoph (Infrared Physics & Technology, 2016)
Local electric defects may result in considerable performance losses in solar cells. Infrared thermography is an essential tool to detect these defects on photovoltaic modules. Accordingly, IR-thermography is frequently used in R&D labs of PV manufactures and, furthermore, outdoors in order to identify faulty modules in PV-power plants. Massive amount of data is acquired which needs to be analyzed. An automatized method for detecting solar modules in IR-images would enable a faster and automatized analysis of the data. However, IR-images tend to suffer from rather large noise, which makes an automatized segmentation challenging. The aim of this study was to establish a reliable segmentation algorithm for R&D labs. We propose an algorithm, which detects a solar cell or module within an IR-image with large noise. We tested the algorithm on images of 10 PV-samples characterized by highly sensitive dark lock-in thermography (DLIT). The algorithm proved to be very reliable in detecting correctly the solar module. In our study, we focused on thin film solar cells, however, a transfer of the algorithm to other cell types is straight forward.
Keywords: DLIT; IR-thermography; Segmentation; Solar module

Autonomous Optimization of Air-Processed Perovskite Solar Cell in a Multidimensional Parameter Space - Zhang, Jiyun; Le Corre, Vincent M.; Wu, Jianchang; Du, Tian; Osterrieder, Tobias; Zhang, Kaicheng; Zhang, Handan; Lüer, Larry; Hauch, Jens; Brabec, Christoph J. (Advanced Energy Materials, 2025)
Traditional optimization methods often face challenges in exploring complex process parameter spaces, which typically result in suboptimal local maxima. Here an autonomous framework driven by a machine learning (ML)-guided automated platform is introduced to optimize the fabrication conditions of additive- and passivation-free perovskite solar cells (PSCs) under ambient conditions. By effectively exploring a 6D parameter space, this method identifies five parameter sets achieving efficiencies above 23%, with a peak efficiency of 23.7% with limited experimental budgets. Feature importance analysis indicates that the rotation speeds during the first and second steps of perovskite processing are the most influential factors affecting device performance, thereby meriting prioritization in the optimization efforts. These results demonstrate the exceptional capability of the autonomous framework in addressing complex process parameter optimization challenges and its potential to advance perovskite photovoltaic technology. Beyond PSCs, this work provides a reliable and comprehensive strategy for optimizing solution-processed semiconductors and highlights the broader applications of autonomous methodologies in materials science.
CRIS-Team Scopus Importer:2025-01-31
Keywords: air-processing perovskite solar cells; automation framework; autonomous optimization; device acceleration platform; machine learning

Axisymmetric and Asymmetric Naphthalene-Bisthienothiophene Based Nonfullerene Acceptors: On Constitutional Isomerization and Photovoltaic Performance - Hu, Wei; Du, Xiaoyan; Zhuang, Wenliu; Su, Wenyan; Cao, Jiamin; Pourrahimi, Amir Masoud; Li, Ning; Shen, Xingxing; Zhang, Maojie; Yu, Donghong; Gruber, Wolfgang; Unruh, Tobias; et al. (ACS Applied Energy Materials, 2020)
Two pairs of constitutional isomers of fused-octacyclic nonfullerene acceptors (NFAs) based on a naphthalene-bisthienothiophene core with or without fluorination at the ending groups have been developed. Compared with the axisymmetric NFAs N66-IC and N66-2FIC with two six-member-ring bridges, their asymmetric constitutional isomers N65-IC and N65-2FIC both with one six-member-ring bridge and one five-member-ring bridge exhibit remarkable red-shifted absorption, higher crystallinity, and slightly down-shifted LUMO energy levels. Organic solar cells based on PBDB-T-2F:N65-2FIC achieved a promising power conversion efficiency of 10.19%, which is three times higher than that of its counterpart PBDB-T-2F:N66-2FIC cell (3.46%). While being blended with PBDB-T as the donor material, the asymmetric acceptor analogue N65-IC based solar cell pronounces a PCE of 9.03%, being significantly improved from that of 5.45% for the PBDB-T:N66-IC based cell, which is in consistency with the results from those cells from their both fluorinated donor and acceptor counterparts. Design rules on either both fluorinated, both nonfluorinated, or cross-combined donor/acceptors for device fabrication has been explored. In addition, PBDB-T-2F:N65-2FIC possesses very promising device stability with 85% of its initial PCE after an exposure time of 1500 h under one sun illumination, which is meaningful for their future commercial devices.<br
Keywords: asymmetry; axisymmetry; isomerization

Balancing electrical and optical losses for efficient 4-terminal Si–perovskite solar cells with solution processed percolation electrodes - Ramírez Quiroz, César Omar; Shen, Yilei; Salvador, Michael Filipe; Forberich, Karen; Schrenker, Nadine; Spyropoulos, Georgios; Heumüller, Thomas; Wilkinson, Benjamin; Kirchartz, Thomas; Spiecker, Erdmann; Verlinden, Pierre J.; Zhang, Xueling; et al. (Journal of Materials Chemistry A, 2018)
The unprecedented rise in efficiency of perovskite-based photovoltaics has sparked interest in semitransparent devices, particularly for tandem structures. Despite promising reports regarding efficiency and reduced parasitic absorption, many devices still rely on processes from the gas phase, compromising both applicability and cost factors. Here, we report all-solution perovskite solar cells with improved infrared transparency ideally suited as top-cells for efficient multi-junction device configurations. We demonstrate the functionality of copper(I) thiocyanate as antireflective layer and as selective contact between the transparent conductive oxide and the perovskite. This concept allows us to fabricate an opaque device with steady state efficiency as high as 20.1%. By employing silver nanowires with robust environmental stability as the bottom electrode, we demonstrate different regimes of device performance that can be described through a classical percolation model, leading to semi-transparent solar cells with efficiencies of up to 17.1%. In conjunction with the implementation of an infrared-tuned transparent conductive oxide contact deposited on UV-fused silica, we show a full device average transmittance surpassing 84% between 800 and 1100 nm (as opposed to 77% with PEDOT:PSS as the selective contact). Finally, we mechanically stacked optimized perovskite devices on top of high performing PERL and IBC silicon architectures. The measured imputed output efficiency of the 4-terminal perovskite–silicon solar cell was 26.7% and 25.2% for the PERL–perovskite and IBC–perovskite, respectivel

Balancing the efficiency, stability, and cost potential for organic solar cells via a new figure of merit - Yang, Wenyan; Wang, Wei; Wang, Yuheng; Sun, Rui; Guo, Jie; Li, Hongneng; Shi, Mumin; Guo, Jing; Wu, Yao; Wang, Tao; Lu, Guanghao; Brabec, Christoph; et al. (Joule, 2021)
In spite of the great success in device efficiency resulting from the excessive design of photovoltaic materials, the stability and cost issues concerning basic commercial requirements of organic solar cells (OSCs) remain unresolved or controversial, slowing down the introduction of market-ready applications. We proposed an exciting discovery that as the active layer thickness decreases, the thermal stability increases gradually, even exceeding 100% of the initial efficiency under 150°C thermal stress. This trend was further confirmed by investigating thermodynamics and kinetics of morphology evolution for PM6:Y6 as a reference example. Extended research found that there is a similar correlation between photo-thermal stability and blend thickness. Consequently, a new reliable industrial figure of merit (i-FOM2.0), including four main factors: efficiency, photo-thermal stability, synthesis complexity, and active layer thickness, is presented here. Our work provides a promising trade-off strategy for reducing efficiency-stability-cost gap and accelerates the commercialization of OSCs.
CRIS-Team Scopus Importer:2021-06-04
Keywords: active layer thickness; figure of merit; organic solar cells; photo-thermal stability; thermal stability

Band-bowing effects in lead-free double Cs2AgBixSb1−xCl6 perovskites and their anion-exchanged derivatives - Stroyuk, Oleksandr; Raievska, Oleksandra; Barabash, Anastasia; Hooper, Riley W.; Michaelis, Vladimir K.; Hauch, Jens; Brabec, Christoph (Journal of Materials Chemistry C, 2023)
Green synthesis of lead-free Cs2AgBixSb1−xCl6 solid-solution double perovskites and their conversion into bromide and iodide derivatives is reported. Interaction of the single-phase Cs2AgBixSb1−xCl6 double perovskites with sodium iodide in 2-propanol/glycerol yields Cs3Bi2xSb2(1−x)I9 derivatives with varied Bi/Sb ratio, while the similar anion exchange with sodium bromide results in mixtures of Cs3Bi2xSb2(1−x)Cl3Br6 and Cs2AgBixSb1−xCl2Br4. A band-bowing effect is revealed for the starting chloride perovskites and the anion-exchange products, with the indirect band gap of intermediate Bi/Sb mixed compounds being significantly lower than the band gaps of corresponding Bi- and Sb-pure products. Solid-state nuclear magnetic resonance spectroscopy uncovered that the band-bowing originates from the lattice disorder of mixed Bi/Sb halide compounds, thus highlighting a new approach for the bandgap design of halide perovskites.
CRIS-Team Scopus Importer:2024-12-16

Bandgap and Photoluminescence Tunability of Lead-Free Cs3Bi2(Br,I)9 Solid Solution Compounds - Hashimoto, Haruto; Oka, Ryohei; Hayakawa, Tomokatsu; Brabec, Christoph (Physica Status Solidi-Rapid Research Letters, 2023)
Herein, lead-free, mixed-halide perovskites of cesium bismuth bromide/iodide are synthesized by a hydrothermal method, and their structures and optical properties of the solid solution compounds are examined. The synthesized compounds exhibit X-ray diffraction patterns similar to that of trigonal Cs3Bi2Br9 (CBB), whose reflections are shifted to lower angles depending on the experimental iodine content. Very interestingly, even with the excessive introduction of iodine content in nominal, the symmetry of the crystals is kept to be trigonal, indicating that bromide CBB and iodide Cs3Bi2I9 (CBI) are crystallographically mixed in a facile way, although the stable crystal form of CBI is hexagonal. The optical properties of bandgap energy Eg and photoluminescence (PL) for the synthesized crystals are also examined. It is found that Eg decreases and PL peak position is correspondingly shifted to a longer wavelength with an increase in the experimental iodine content due to their band-to-band transitions. Moreover, first-principles calculation suggests the reduction of Eg with iodine content and the varied nature of band structure from direct (trigonal CBB) to indirect (trigonal CBI) transition. These novel findings can make the proposed strategy successful for developing lead-free, mixed-halide Bi-based perovskite crystals with the tunability of their optical properties.
CRIS-Team Scopus Importer:2023-09-22
Keywords: bandgap tunability; Bi-based halide perovskites; electronic structures; hydrothermal synthesis; photoluminescence; solid solution compounds; trigonal

Barix multilayer barrier technology for organic solar cells - Moro, Lorenza; Rutherford, Nicole M.; Visser, Robert Jan; Hauch, Jens A.; Klepek, Claudia; Denk, Patrick; Schilinsky, Pavel; Brabec, Christoph (Proc. of SPIE Vol. 6334, 2006)
The effect of multilayer barrier materials on the lifetime of organic photovoltaic cells has been investigated. For thin film encapsulated cells a protective layer was used to prevent damage during barrier layer deposition. No post deposition effects developed after dry box storage. In accelerated temperature and humidity lifetime testing the degradation of the encapsulated cells can be related to the loss of effective cell area. An extrapolation of the lifetime at room conditions has been quantitatively determined by comparing the cell degradation with the loss of Ca in a Caoxidation test. The results indicate a barrier permeation rate of 10 gr /[m* day] for these samples, corresponding to a lifetime of greater than 5000 hours. Routes to improvement of the OPV cell lifetime are discussed.
Keywords: Barrier films; Barrier layers; Bulk heterojunction; Conjugated polymers; Degradation; Encapsulation; Organic solar cells

Basal plane dislocation dynamics in highly p-type doped versus highly n-type doped SiC - Wellmann, Peter; Queren, Desiree; Müller, Ralf; Sakwe, Aloysius; Künecke, Ulrike (Materials Science Forum, 2006)
The long term performance of today's Sic based bipolar power devices suffer strongly from stacking fault formation caused by slip of basal plane dislocations, the latter often originating from the n-type doped Sic substrate wafer. In this paper, using sequentially p-type/n-type/p-type doped Sic crystals, we address the question, whether basal plane dislocation generation and annihilation behaves differently in n-type and p-type Sic. We have found that basal plane dislocations are absent or at least appear significantly less pronounced in p-type doped Sic, which may become of great importance for the stacking fault problem in si
Keywords: p-type SiC; dislocations; stacking faults; bipolar devices

Beginner's Guide to Visual Analysis of Perovskite and Organic Solar Cell Current Density–Voltage Characteristics - These, Albert; Koster, L. Jan Anton; Brabec, Christoph; Le Corre, Vincent Marc (Advanced Energy Materials, 2024)
The current density–voltage characteristic (J–V) is a critical tool for understanding the behavior of solar cells. This study presents an overview of the key aspects of J–V analysis and introduces a user-friendly flowchart that facilitates the swift identification of the most probable limiting process in a solar cell, based mainly on the outcomes of light-intensity-dependent J–V measurements. The flowchart is developed through extensive drift-diffusion simulations and a rigorous review of the literature, with a specific focus on perovskite and organic solar cells. Moreover, the flowchart proposes supplementary experiments that can be conducted to obtain a more precise prediction of the primary performance losses. It therefore serves as an optimal starting point to analyse performance losses of solar cells.
CRIS-Team Scopus Importer:2024-04-19
Keywords: current-voltage characteristic; drift-diffusion simulation; organic solar cell; perovskite solar cell; photovoltaics

Beyond Donor-Acceptor (D-A) Approach: Structure-Optoelectronic Properties-Organic Photovoltaic Performance Correlation in New D-A1-D-A2 Low-Bandgap Conjugated Polymers - Chochos, Christos L.; Drakopoulou, Sofia; Katsouras, Athanasios; Squeo, Benedetta M.; Sprau, Christian; Colsmann, Alexander; Gregoriou, Vasilis G.; Cando, Alex Palma; Allard, Sybille; Scherf, Ullrich; Gasparini, Nicola; Kazerouni, Negar; et al. (Macromolecular Rapid Communications, 2017)
Low-bandgap near-infrared polymers are usually synthesized using the common donor-acceptor (D-A) approach. However, recently polymer chemists are introducing more complex chemical concepts for better fine tuning of their optoelectronic properties. Usually these studies are limited to one or two polymer examples in each case study so far, though. In this study, the dependence of optoelectronic and macroscopic (device performance) properties in a series of six new D-A-D-A low bandgap semiconducting polymers is reported for the first time. Correlation between the chemical structure of single-component polymer films and their optoelectronic properties has been achieved in terms of absorption maxima, optical bandgap, ionization potential, and electron affinity. Preliminary organic photovoltaic results based on blends of the D-A-D-A polymers as the electron donor mixed with the fullerene derivative [6,6]-phenyl-C-butyric acid methyl ester demonstrate power conversion efficiencies close to 4% with short-circuit current densities (J ) of around 11 mA cm, high fill factors up to 0.70, and high open-circuit voltages (V s) of 0.70 V. All the devices are fabricated in an inverted architecture with the photoactive layer processed in air with doctor blade technique, showing the compatibility with roll-to-roll large-scale manufacturing processes.
Keywords: Conjugated polymers; Donor-acceptor; Low bandgap; Near-infrared; Organic photovoltaics

Beyond Ternary OPV: High-Throughput Experimentation and Self-Driving Laboratories Optimize Multicomponent Systems - Langner, Stefan; Häse, Florian; Perea, Jose Dario; Stubhan, Tobias; Hauch, Jens; Roch, Loïc M.; Heumüller, Thomas; Aspuru-Guzik, Alán; Brabec, Christoph (Advanced Materials, 2020)
Fundamental advances to increase the efficiency as well as stability of organic photovoltaics (OPVs) are achieved by designing ternary blends, which represents a clear trend toward multicomponent active layer blends. The development of high-throughput and autonomous experimentation methods is reported for the effective optimization of multicomponent polymer blends for OPVs. A method for automated film formation enabling the fabrication of up to 6048 films per day is introduced. Equipping this automated experimentation platform with a Bayesian optimization, a self-driving laboratory is constructed that autonomously evaluates measurements to design and execute the next experiments. To demonstrate the potential of these methods, a 4D parameter space of quaternary OPV blends is mapped and optimized for photostability. While with conventional approaches, roughly 100 mg of material would be necessary, the robot-based platform can screen 2000 combinations with less than 10 mg, and machine-learning-enabled autonomous experimentation identifies stable compositions with less than 1 mg.
CRIS-Team Scopus Importer:2020-02-25
Keywords: high-throughput experimentation; machine learning; organic photovoltaics; photostability; solar energy

Bilayer–ternary polymer solar cells fabricated using spontaneous spreading on water - Colberts, Fallon JM; Wienk, Martijn M; Heuvel, Ruurd; Li, Weiwei; Le Corre, Vincent Marc; Koster, L Jan Anton; Janssen, René AJ (Advanced Energy Materials, 2018)

Bimolecular crystals of fullerenes in conjugated polymers and the implications of molecular mixing for solar cells - Mayer, A.C.; Toney, M.F.; Scully, S.R.; Rivnay, J.; Brabec, Christoph; Scharber, Markus C.; Koppe, Markus; Heeney, Martin; Mcculloch, Iain; Mcgehee, Michael D. (Advanced Functional Materials, 2009)
The performance of polymerfullerene bulk heterojunction solar cells is heavily influenced by the interpenetrating nanostructure formed by the two semiconductors because the size of the phases, the nature of the interface, and molecular packing affect exciton dissociation, recombination, and charge transport. Here, X-ray diffraction is used to demonstrate the formation of stable, well-ordered bimolecular crystals offullerene intercalated between the side-chains of the semiconducting polymer poly(2,5-bis(3-tetradecylthiophen- 2-yl)thieno[3,2-b]thiophene. It is shown that fullerene intercalation is general and is likely to occur in blends with both amorphous and semicrystalline polymers when there is enough free volume between the side-chains to accommodate the fullerene molecule. These findings offer explanations for why luminescence is completely quenched in crystals much larger than exciton diffusion lengths, how the hole mobility of poly(2-methoxy-5-(3',7'- dimethyloxy)-p-phylene vinylene) increases by over 2 orders of magnitude when blended with fullerene derivatives, and why large-scale phase separation occurs in some polymer:fullerene blend ratios while thermodynamically stable mixing on the molecular scale occurs for others. Furthermore, it is shown that intercalation offullerenes between side chains mostly determines the optimum polymer:fullerene blending ratios. These discoveries suggest a method ofintentionally designing bimolecular crystals and tuning their properties to create novel materials for photovoltaic and other applications. © 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Binary cations minimize energy loss in the wide-band-gap perovskite toward efficient all-perovskite tandem solar cells - Zhang, Kaicheng; Liu, Chao; Peng, Zijian; Li, Chaohui; Tian, Jingjing; Li, Canru; García Cerrillo, José; Dong, Lirong; Streller, Fabian; Späth, Andreas; Musiienko, Artem; Englhard, Jonas; et al. (Joule, 2024)
Perovskite-based tandem solar cells stand at the forefront of photovoltaic innovation due to their exceptional performance and cost-effective fabrication. This study focuses on minimizing energy losses within a 1.80 eV perovskite sub-cell. We demonstrate that the surface treatment of perovskite with binary guanidinium bromide and 4-fluorophenylammonium iodide synergistically reduces defect densities and adjusts interfacial energy-level alignment. The enhanced passivation effect and the formation of a surface dipole significantly reduce nonradiative recombination and transport losses, leading to a notable increase in the open-circuit voltage and fill factor product, thereby achieving an impressive power conversion efficiency (PCE) of 19.0%. The reproducibility of these findings is confirmed by consistent results across different laboratories. Furthermore, integration with a narrow-band-gap perovskite yields an all-perovskite tandem device with a PCE of 27.2%. This comprehensive understanding of the pivotal role of spacer cations in surface treatment significantly advances the pathway toward efficient perovskite photovoltaics.
CRIS-Team Scopus Importer:2024-08-30
Keywords: 2D phases; all-perovskite tandem solar cell; energy loss; energy-level alignment; nonradiative recombination; passivation; spacer cations; surface dipole; surface treatment; wide band-gap perovskite

Bioinspired Design of SrAl2O4:Eu2+ Phosphor - Kostova, Marya H.; Zollfrank, Cordt; Batentschuk, Miroslaw; Götz-Neunhoeffer, Friedlinde; Winnacker, Albrecht; Greil, Peter (Advanced Functional Materials, 2009)
A phosphor based on Sr0.97Al2O4:Eu 0.03 with a biomorphous morphology is manufactured via vacuum assisted infiltration of wood tissue [Pinus sylvestris) with a precursor nitrate solution. The nitrate solution penetrates homogeneously into the uniform arrangement of rectangular shaped tracheidal cells of the wood tissue. According to scanning electron microscopy, the original wood cell walls are completely transformed retaining the original wood structure. The major crystalline phase is monoclinic SrAl2O4, detected by X-ray diffraction and confirmed by Rietveld refinement. Energy-dispersive X-ray analysis proves the homogeneous conversion of the original wood cell wall into Sr 0.97Al2O4:Eu0.03 struts. The optical properties of the resulting phosphor material are determined by photoluminescence and cathode-luminescence spectroscopy in scanning electron microscopy. The biotemplated Sr0.97Al2O 4IEU0.03 shows a characteristic green emission at 530 nm (2.34 eV). Shaping biomorphous SrAl2O4:Eu2+ phosphor with a microstructure pseudomorphous to the bioorganic template anatomy offers a novel approach for designing micropatterned phosphor materials. © 2009 WILEY-VCH Verlag GmbH & Co. KCa
UnivIS-Import:2015-03-09:Pub.2009.nat.dgeo.IGM.LM.bioins

Biotemplating of BaFBr:Eu2+ for X-ray storage phosphor applications - Kostova, Marya H.; Batentschuk, Miroslaw; Götz-Neunhoeffer, Friedlinde; Gruber, Sabine; Winnacker, Albrecht; Greil, Peter; Zollfrank, Cordt (Materials Chemistry and Physics, 2010)
The design of hierarchically patterned novel structures by replicating the cellular tissue of wood has recently attained increasing interest. X-ray storage phosphor BaFBr:Eu2+ is manufactured via vacuum assisted repeated infiltration of wood tissue (Pinus sylvestris). A submicrometer precipitate is formed via wet chemical reaction of NH4F, BaBr2·2H2O and EuCl3·6H2O in methanol. According to scanning electron microscopy (SEM) and energy dispersive X-ray analysis (EDX), the original wood cell walls are filled with the precipitate and completely transformed into BaFBr struts after sintering at 800 °C. The optical properties of the biomorphous phosphor microstructure are determined by photoluminescence spectroscopy (PL) at room temperature, photo-stimulated luminescence spectroscopy (PSL) and cathodoluminescence spectroscopy (CL) in the SEM. A broadening of the PSL peak is observed and ascribed to the incorporation of calcium impurities present in the pine wood tissue. The potential of biotemplates for generating highly oriented and optically isolated μm- and sub-μm matrix of X-ray storage phosphor material is illustrated.
UnivIS-Import:2015-03-09:Pub.2010.nat.dgeo.IGM.LM.biotem
Keywords: Optical properties; Biotemplating; X-ray storage phosphor

Bipolar charge transport in PCPDTBT-PCBM bulk-heterojunctions for photovoltaic applications - Morana, Mauro; Wegscheider, Matthias; Bonanni, Alberta; Kopidakis, Nikos; Shaheen, Sean; Scharber, Markus; Zhu, Zhengguo; Waller, David; Gaudiana, Russell; Brabec, Christoph (Advanced Functional Materials, 2008)
An experimental study of the transport properties of a low-bandgap conjugated polymer giving high photovoltaic quantum efficiencies in the near infrared spectral region (Eg-opt similar to 1.35 eV) is presented. Using a organic thin film transistor geometry, we demonstrate a relatively high in-plane hole mobility, up to 1.5. x 10(-2) cm(2) V-1 s(-1) and quantify the electron mobility at 3 x .10(-5) cm(2) V-1 s(-1) on a SiO2 dielectric. In addition, singular contact behavior results in bipolar quasi-Ohmic injection both from low and high workfunction metals like LiF/Al and An. X-ray investigations revealed a degree of interchain pi-stacking that is probably embedded in a disordered matrix. Disorder also manifests itself in a strong positive field dependence of the hole mobility from the electric field. In blends made with the electron acceptor methanofullerene [6,6]-phenyl C-61 butyric acid methyl ester (PCBM), the transistor characteristics suggest a relatively unfavorable intermixing of the two components for the application to photovoltaic devices. We attribute this to a too fine dispersion of [C60]-PCBM in the polymer matrix, that is also confirmed by the quenching of the photoluminescence signal measured in PCPDTBT [C60]-PCBM films with various composition. We show that a higher degree of phase separation can be induced during the film formation by using 1,8-octanedithiol (ODT), which leads to a more efficient electron percolation in the [C60]-PCBM. In addition, the experimental results, in combination with those of solar cells seem to support the correlation between the blend morphology and charge recombination. We tentatively propose that the drift length, and similarly the electrical fill factor, can be limited by the recombination of holes with electrons trapped on isolated [C60]-PCBM clusters. Ionized and isolated [C60]-PCBM molecules can modify the local electric field in the solar cell by build-up of a space-charge. The results also suggest that further improvements of the fill factor may also be limited by a strong electrical-field dependence of the hole transport.

"Black" TiO2 Nanotubes Formed by High-Energy Proton Implantation Show Noble-Metal-co-Catalyst Free Photocatalytic H2-Evolution - Frey, Lothar; Osvet, Andres; Zhou, Xuemei; Haeublein, Volker; Schmuki, Patrik; Frey, Lothar; Spiecker, Erdmann; Mackovic, Mirza; Liu, Ning; Hartmann, Martin; Nakajima, Tomohiko; Venkatesan, Uma Maheswari (Nano Letters, 2015)
We apply high-energy proton ion-implantation to modify TiO nanotubes selectively at their tops. In the proton-implanted region, we observe the creation of intrinsic cocatalytic centers for photocatalytic H-evolution. We find proton implantation to induce specific defects and a characteristic modification of the electronic properties not only in nanotubes but also on anatase single crystal (001) surfaces. Nevertheless, for TiO nanotubes a strong synergetic effect between implanted region (catalyst) and implant-free tube segment (absorber) can be obtained.
Keywords: ion-implantation; Nanotubes; photocatalysts; self-organization; titania; water-splitting

Bottom Contact Engineering for Ambient Fabrication of >25% Durable Perovskite Solar Cells - Yuan, Ligang; Zou, Shibing; Zhang, Kaicheng; Huang, Peng; Dong, Yuyan; Wang, Jiarong; Fan, Kezhou; Lam, Man Yu; Wu, Xiao; Cheng, Wei; Tang, Ruijia; Chen, Wenhao; et al. (Advanced Materials, 2024)
The bottom contact in perovskite solar cells (PSCs) is easy to cause deep trap states and severe instability issues, especially under maximum power point tracking (MPPT). In this study, sodium gluconate (SG) is employed to disperse tin oxide (SnO2) nanoparticles (NPs) and regulate the interface contact at the buried interface. The SG-SnO2 electron transfer layer (ETL) enabled the deposition of pinhole-free perovskite films in ambient air and improved interface contact by bridging effect. SG-SnO2 PSCs achieved an impressive power conversion efficiency (PCE) of 25.34% (certified as 25.17%) with a high open-circuit voltage (VOC) exceeding 1.19 V. The VOC loss is less than 0.34 V relative to the 1.53 eV bandgap, and the fill factor (FF) loss is only 2.02% due to the improved contact. The SG-SnO2 PSCs retained around 90% of their initial PCEs after 1000 h operation (T90 = 1000 h), higher than T80 = 1000 h for the control SnO2 PSC. Microstructure analysis revealed that light-induced degradation primarily occurred at the buried holes and grain boundaries and highlighted the importance of bottom-contact engineering.
CRIS-Team Scopus Importer:2024-08-09
Keywords: bottom contact; perovskite solar cell; photodegradation; SnO; sodium gluconate

Branched side chains improve molecular packing of non-fullerene acceptors - Li, Ning; Brabec, Christoph (Science China-Chemistry, 2021)
CRIS-Team Scopus Importer:2021-06-25

Bridging theory and experiment in defect-tolerant semiconductors for photovoltaics - Hammer, Maria; Schlott, Hannah; Lüer, Larry; Brabec, Christoph; Sytnyk, Mykhailo; Will, Johannes; Meyer, Bernd; Heiß, Wolfgang (Nature Reviews Materials, 2025)
Defect tolerance is a concept applied in photovoltaics to explain semiconductors such as lead-halide perovskites that excel without relying on single-crystalline growth. It differentiates from the mere absence of defects, emphasizing on minimizing the influence of defects on minority carrier lifetimes. Whether defect tolerance is the only reason for the superiority of lead-halide-perovskite-based solution-processed solar cells is still controversial. However, the defect tolerance of various semiconductor structures and materials has been experimentally suggested and, in some cases, proven. In this Perspective, we explore defect tolerance across material science, defect characterization and computational modelling. With a primary focus on electrically or optically active defects, we systematically compare computational and experimental results from the literature. We aim to address the complexity arising from diverse theoretical approaches that have yielded partially contradictory results. Additionally, experimental findings have been subject to varied interpretations, ranging from defect signals to ion migration. We endeavour to chart a course through this intricacy and seek to establish a rigorous framework for the identification and quantitative assessment of defect toleranc

Brightly Luminescent and Color-Tunable CsPbBr3 Nanocrystals with Enhanced Stability and Room Temperature Cubic Structure through Codoping with MnCl2 - Darwish, Elshaimaa; Elia, Jack; Fehn, Dominik; Köllner, David; Pourjafar, Amir; Christiansen, Silke; Meyer, Karsten; Webber, Kyle Grant; Brabec, Christoph; Batentschuk, Miroslaw; Osvet, Andres (Advanced Engineering Materials, 2024)
Lead halide perovskites have attracted much attention from the scientific community in recent years due to their attractive properties and their proven potential in many applications. Nevertheless, their stability and lead toxicity have remained a problem. Herein, the potential of manganese as a divalent dopant to offer better stability and replace a fraction of the toxic lead ions is investigated. Moreover, the reverse microemulsion method is used to obtain tunability in emission and bandgap by doping cesium lead bromide. Furthermore, cubic cesium lead bromide particles are managed to obtain at room temperature as a result of doping.
CRIS-Team Scopus Importer:2024-05-24
Keywords: light conversion; perovskite nanoparticle; semiconductor quantum dots

Brightly Luminescent and Color-Tunable Formamidinium Lead Halide Perovskite FAPbX3 (X = Cl, Br, I) Colloidal Nanocrystals - Levchuk, Ievgen; Osvet, Andres; Tang, Xiaofeng; Brandl, Marco; Perea, Jose Dario; Högl, Florian; Matt, Gebhard; Hock, Rainer; Batentschuk, Miroslaw; Brabec, Christoph (Nano Letters, 2017)
In the past few years, hybrid organic-inorganic and all-inorganic metal halide perovskite nanocrystals have become one of the most interesting materials for optoelectronic applications. Here, we report a facile and rapid room temperature synthesis of 15-25 nm formamidinium CH(NH2)2PbX3 (X = Cl, Br, I, or mixed Cl/Br and Br/I) colloidal nanocrystals by ligand-assisted reprecipitation (LARP). The cubic and platelet-like nanocrystals with their emission in the range of 415-740 nm, full width at half-maximum (fwhm) of 20-44 nm, and radiative lifetimes of 5-166 ns enable band gap tuning by halide composition as well as by their thickness tailoring; they have a high photoluminescence quantum yield (up to 85%), colloidal and thermodynamic stability. Combined with surface modification that prevents degradation by water, this nanocrystalline material is an ideal candidate for optoelectronic devices and applications. In addition, optoelectronic measurements verify that the photodetector based on FAPbI3 nanocrystals paves the way for perovskite quantum dot photovoltaics. © 2017 American Chemical Society.
Keywords: Chelation; Energy gap; Hybrid materials; Ligands; Metal halides; Nanocrystalline materials; Optoelectronic devices; Perovskite; Photoluminescence; Semiconductor quantum dots; Surface treatment; Colloidal nanocrystals; Formamidinium; Hybrid organic-inorganic; Optoelectronic applications; Optoelectronic measurements; Photoluminescence quantum yields; Re-precipitation; Room temperature synthesis; Nanocrystals

Broadband and omnidirectional light harvesting enhancement of fluorescent SiC - Ou, Yiyu; Jokubavicius, Valdas; Hens, Philip; Kaiser, Michl; Wellmann, Peter; Yakimova, Rositza; Syväjärvi, Mikael; Ou, Haiyan (Optics Express, 2012)
In the present work, antireflective sub-wavelength structures have been fabricated on fluorescent 6H-SiC to enhance the white light extraction efficiency by using the reactive-ion etching method. Broadband and omnidirectional antireflection characteristics show that 6H-SiC with antireflective sub-wavelength structures suppress the average surface reflection significantly from 20.5 % to 1.01 % over a wide spectral range of 390-784 nm. The luminescence intensity of the fluorescent 6H-SiC could be enhanced in the whole emission angle range. It maintains an enhancement larger than 91 % up to the incident angle of 70 degrees, while the largest enhancement of 115.4 % could be obtained at 16 degrees. The antireflective sub-wavelength structures on fluorescent 6H-SiC could also preserve the luminescence spectral profile at a large emission angle by eliminating the Fabry-Perot microcavity interference effect. (C) 2012 Optical Society of America
Keywords: Nanostructure fabrication; Photoluminescence; Subwavelength structures; Nanostructures.

Broadening of Distribution of Trap States in PbS Quantum Dot Field-Effect Transistors with High-k Dielectrics - Nugraha, Mohamad I.; Hausermann, Roger; Watanabe, Shun; Matsui, Hiroyuki; Sytnyk, Mykhailo; Heiß, Wolfgang; Takeya, Jun; Loi, Maria A. (ACS Applied Materials and Interfaces, 2017)
We perform a quantitative analysis of the trap density of states (trap DOS) in PbS quantum dot field-effect transistors (QD-FETs), which utilize several polymer gate insulators with a wide range of dielectric constants. With increasing gate dielectric constant, we observe increasing trap DOS close to the lowest unoccupied molecular orbital (LUMO) of the QDs. In addition, this increase is also consistently followed by broadening of the trap DOS. We rationalize that the increase and broadening of the spectral trap distribution originate from dipolar disorder as well as polaronic interactions, which are appearing at strong dielectric polarization. Interestingly, the increased polaron-induced traps do not show any negative effect on the charge carrier mobility in our QD devices at the highest applied gate voltage, giving the possibility to fabricate efficient low-voltage QD devices without suppressing carrier transport.
Keywords: field-effect transistors; high-k; PbS quantum dots; polaron; trap states

Building process design rules for microstructure control in wide-bandgap mixed halide perovskite solar cells by a high-throughput approach - Akhundova, Fatima; Lüer, Larry; Osvet, Andres; Hauch, Jens; Peters, Ian Marius; Forberich, Karen; Li, Ning; Brabec, Christoph (Applied Physics Letters, 2021)
Wide bandgap mixed halide perovskites ABX3, in which X can be I, Br, or Cl, are promising materials to form highly efficient optoelectronic devices, because the optical bandgap can be controlled over a wide range by variation of the halogen composition. However, significant nonradiative losses must be overcome to approach the efficiency limit of single-junction solar cells. Here, we present a high throughput-based investigation of the influence of processing parameters on nonradiative losses in the perovskite bulk. We perform antisolvent crystallization during spin coating and vary the solvent type, its volume, and the temperature of the subsequent annealing step. We use the photoluminescence quantum yield (PLQY) as a proxy to the presence of nonradiative losses and PL spectra as a qualitative probe for sample morphology. Using Gaussian process regression, we find that we can reliably predict PLQY from the PL spectral shape. This means that the PL spectral shape conveys the essential photophysics controlling PL quenching and thus nonradiative charge recombination. In comparison with scanning electron micrographs and x-ray diffraction data, we find that nonradiative losses in polycrystalline perovskite films are caused by increased domain size dispersion. Our method provides a simple and fast structure-sensitive in-line probe for fast morphology optimization in a high-throughput fashion.
CRIS-Team Scopus Importer:2021-06-25

Bulk growth of SiC - Wellmann, Peter; Müller, Ralf; Sakwe, Aloysius; Künecke, Ulrike; Hens, Philip; Stockmeier, Matthias; Konias, Katja; Hock, Rainer; Magerl, Andreas; Pons, Michel (Materials Research Society Symposium - Proceedings, 2008)
The paper reviews the basics of SiC bulk growth by the physical vapor transport (PVT) method and discusses current and possible future concepts to improve crystalline quality. In-situ process visualization using x-rays, numerical modeling and advanced doping techniques will be briefly presented which support growth process optimization. The ,,pure" PVT technique will be compared with related developments like the so called Modified-PVT, Continuous-Feeding-PVT, High-Temperature-CVD and Halide-CVD. Special emphasis will be put on dislocation generation and annihilation and concepts to reduce dislocation density during SiC bulk crystal growth. The dislocation study is based on a statistical approach. Rather than following the evolution of a single defect, statistic data which reflect a more global dislocation density evolution are interpreted. In this context a new approach will be presented which relates thermally induced strain during growth and dislocation patterning into network
Keywords: Silicon carbide; bulk growth; physical vapor transport (PVT); in-situ visualization; numerical modeling; doping; dislocations; strain

Bulk growth of SiC - review on advances of SiC vapor growth for improved doping and systematic study on dislocation evolution - Sakwe, Aloysius; Stockmeier, Matthias; Hens, Philip; Müller, Ralf; Queren, Desiree; Künecke, Ulrike; Konias, Katja; Hock, Rainer; Magerl, Andreas; Pons, Michel; Winnacker, Albrecht; Wellmann, Peter (physica status solidi (b), 2008)
The paper reviews research on advanced crystal growth of SiC. A brief review highlights the benefits of the so called Modified Physical Vapor Transport Technique which uses an additional gas pipe for fine tuning of the growth cell of a conventional Physical Vapor Transport setup with additional gases. Main emphasis, however, will be laid on a systematic dislocation evolution study for various growth parameter sets. Besides doping, growth temperature was considered. Two main results were found: (i) In p-type SiC, irrespective of the incorporation of aluminum or boron acceptors, basal plane dislocations that are harmful for bipolar power devices appear less pronounced or are even absent compared to n-type SiC. (ii) Growth at elevated seed temperature (i.e. 2300 degrees C and higher) is beneficial for low dislocation densities. (C) 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
Keywords: Crystal growth; bulk; silicon carbide; SiC; Modified Physical Vapor Transport (MPVT); dislocations; basal plane dislocations; doping; growth temperature

Burn-in Free Nonfullerene-Based Organic Solar Cells - Gasparini, Nicola; Salvador, Michael Filipe; Strohm, Sebastian; Heumüller, Thomas; Levchuk, Ievgen; Wadsworth, Andrew; Bannock, James H.; de Mello, John C.; Egelhaaf, Hans Joachim; Baran, Derya; Mcculloch, Iain; Brabec, Christoph (Advanced Energy Materials, 2017)
Organic solar cells that are free of burn-in, the commonly observed rapid performance loss under light, are presented. The solar cells are based on poly(3-hexylthiophene) (P3HT) with varying molecular weights and a nonfullerene acceptor (rhodanine-benzothiadiazole-coupled indacenodithiophene, IDTBR) and are fabricated in air. P3HT:IDTBR solar cells light-soaked over the course of 2000 h lose about 5% of power conversion efficiency (PCE), in stark contrast to [6,6]-Phenyl C61 butyric acid methyl ester (PCBM)-based solar cells whose PCE shows a burn-in that extends over several hundreds of hours and levels off at a loss of ≈34%. Replacing PCBM with IDTBR prevents short-circuit current losses due to fullerene dimerization and inhibits disorder-induced open-circuit voltage losses, indicating a very robust device operation that is insensitive to defect states. Small losses in fill factor over time are proposed to originate from polymer or interface defects. Finally, the combination of enhanced efficiency and stability in P3HT:IDTBR increases the lifetime energy yield by more than a factor of 10 when compared with the same type of devices using a fullerene-based acceptor instead. © 2017 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
Keywords: Butyric acid; Defects; Degradation; Fullerenes; Open circuit voltage; Organic solar cells; Enhanced efficiency; Light soaking; Nonfullerene acceptor; Open circuit voltage loss; P3HT; Poly-3-hexylthiophene; Power conversion efficiencies; [6; 6]-phenyl-C61-butyric acid methyl esters; Solar cells

Bypassing the Single Junction Limit with Advanced Photovoltaic Architectures - Lüer, Larry; Peters, Ian Marius; Le Corre, Vincent Marc; Forberich, Karen; Guldi, Dirk Michael; Brabec, Christoph (Advanced Materials, 2023)
Multijunction devices and photon up- and down-conversion are prominent concepts aimed at increasing photovoltaic efficiencies beyond the single junction limit. Integrating these concepts into advanced architectures may address long-standing issues such as processing complexity, microstructure control, and resilience against spectral changes of the incoming radiation. However, so far, no models have been established to predict the performance of such integrated architectures. Here, a simulation environment based on Bayesian optimization is presented, that can predict and virtually optimize the electrical performance of multi-junction architectures, both vertical and lateral, in combination with up- and down-conversion materials. Microstructure effects on performance are explicitly considered using machine-learned predictive models from high throughput experimentation on simpler architectures. Two architectures that would surpass the single junction limit of photovoltaic energy conversion at reasonable complexity are identified: a vertical “staggered half octave system,” where selective absorption allows the use of 6 different bandgaps, and the lateral “overlapping rainbow system” where selective irradiation allows the use of a narrowband energy acceptor with reduced voltage losses, according to the energy gap law. Both architectures would be highly resilient against spectral changes, in contrast with two terminal multi-junction architectures which are limited by Kirchhoff's law.<br

Cage Molecules Stabilize Lead Halide Perovskite Thin Films - Sun, Shijing; Liu, Ming; Thapa, Janak; Hartono, Noor Titan Putri; Zhao, Yicheng; He, Donglin; Wieghold, Sarah; Chua, Matthew; Wu, Yue; Bulović, Vladimir; Ling, Sanliang; Brabec, Christoph; et al. (Chemistry of Materials, 2022)
The environmental stability of hybrid organic-inorganic perovskite (HOIP) materials needs to increase to enable their widespread adoption in thin-film solar and optoelectronic devices. Molecular additives have recently emerged as an effective strategy for regulating HOIP crystal growth and passivating defects. However, to date the choice of additives is largely limited to a dozen or so materials under the design philosophy that high crystallinity is a prerequisite for stable HOIP thin films. In this study, we incorporate porous organic cages (POCs) as functional additives into perovskite thin films for the first time and investigate the HOIP-POC interaction via a combined experimental and computational approach. POCs are significantly larger than the small-molecule additives explored for HOIP synthesis to date but much smaller than polymeric sealants. Partially amorphized composites of MAPbI3 (methylammonium lead iodide, HOIP) and RCC3 (an amine POC) form a network-like surface topography and lead to an increase in the optical bandgap from 1.60 to 1.63 eV. Further in situ optical imaging suggests that RCC3 can delay the MAPbI3 film degradation onset up to 50× under heat and humidity stresses, showing promise for improving reliability in HOIP-based solar-cell and light-emitting applications. Furthermore, there is evidence of molecular interactions between RCC3 and MAPbI3, as fingerprinted by the suppressed N-H stretching mode in MA+ from Fourier transform infrared (FTIR) spectra and density functional theory (DFT) simulations that suggest strong hydrogen bonding between MA+ and RCC3. Given the diversity of POCs and HOIPs, our work opens a new avenue to stabilize HOIPs via tailored molecular interactions with functional organic materials.
CRIS-Team Scopus Importer:2022-11-11

Capacitive Dark Currents, Hysteresis, and Electrode Polarization in Lead Halide Perovskite Solar Cells - Almora Rodriguez, Osbel; Zarazua, Isaac; Mas-Marza, Elena; Mora-Sero, Ivan; Bisquert, Juan; Garcia-Belmonte, Germà (Journal of Physical Chemistry Letters, 2015)
Despite spectacular advances in the conversion efficiency of perovskite solar cells many aspects of its operating modes are still poorly understood. Capacitance constituted to explore which mechanisms and functions. Analyzing capacitive responses in the device but also the kinetics of the charging processes and how they alter the solar cell current. Two main polarization processes are identified. Dielectric properties of the microscopic dipolar units through the orthorhombic-to-tetragonal phase transition account. Electrode polarization caused by interfacial effects, presumably related to kinetically slowness piled up in the vicinity of the outer interfaces, consistently explain the reported excess capacitance values ​​at low frequencies. In addition, current-voltage curves and capacitive responses of perovskite-based solar cells are connected. The observed hysteretic effect in the dark current originates from the slow capacitive mechanisms.<br
Keywords: Photovoltaics; lead halide perovskites; hysteresis; capacitance; electrode polarization

Carbon Photodetectors: The Versatility of Carbon Allotropes - Richter, Moses; Heumüller, Thomas; Matt, Gebhard; Heiß, Wolfgang; Brabec, Christoph; Heiß, Wolfgang (Advanced Energy Materials, 2016)
Carbon-based organic electronics are a technology, with the potential of complementing and substituting opto-electronic devices based on inorganic semiconductors and metals. In the group of organic semiconductors, carbon allotropes come with outstanding opto-electric properties and are remarkable candidates for novel applications like printed electronics via solution-processing on mechanically flexible, robust and light weight substrates, while reducing the environmental impact. Carbon allotropes like fullerenes, graphene quantum dots (GQD), carbon nanotubes (CNT), graphene and also diamond are especially interesting for photodetectors due to their tunable bandgap, high absorption coefficients and high charge carrier mobilites. These unique opto-electric properties of the allotropes, which strongly depend on their molecular dimensionality (0D, 1D, 2D and 3D), allow each allotrope to be used in a preferential range. Hence, relying on the intrinsic properties of carbon allotropes or by hybridization, carbon-based photodetectors are built for a spectral bandwidth, reaching from gamma-rays to THz radiation. This review highlights the recent advances in photodetectors based on fullerenes, GQDs, CNTs, graphene and diamond, with the focus on room temperature-operated devices. The versatility of multi-dimensional carbon allotropes is outstanding, and promising results outline the maturing of all carbon-based photodetection across the technologically relevant wavelengths.
Keywords: Carbon nanotubes; Fullerenes; Graphene; Graphene quantum dots; Organic photodetectors

Carrier Lifetimes and Influence of In-Grown Defects in N-B Co-Doped 6H-SiC - Grivickas, Vytautas; Gulbinas, Karolis; Jokubavicius, Valdas; Sun, Jianwu; Karaliūnas, Mindaugas; Kamiyama, Satoshi; Linnarsson, Margareta K.; Kaiser, Michl; Wellmann, Peter; Syväjärvi, Mikael (IOP Conference Series: Materials Science and Engineering, 2014)
The thick N-B co-doped epilayers were grown by the fast sublimation growth method and the depth-resolved carrier lifetimes have been investigated by means of the free-carrier absorption (FCA) decay under perpendicular probe-pump measurement geometry. In some samples, we optically reveal in-grown carbon inclusions and polycrystalline defects of substantial concentration and show that these defects slow down excess carrier lifetime and prevent donor-acceptor pair photoluminescence (DAP PL). A pronounced electron lifetime reduction when injection level approaches the doping level was observed. It is caused by diffusion driven non-radiative recombination. However, the influence of surface recombination is small and insignificant at 300
Keywords: SiC; sublimation growth; carrier lifetime; co-doped epilayers

Carrier Transport and Recombination in Efficient "All-Small-Molecule" Solar Cells with the Nonfullerene Acceptor IDTBR - Liang, Ru‐Ze; Babics, Maxime; Savikhin, Victoria; Zhang, Weimin; Le Corre, Vincent Marc; Lopatin, Sergei; Kan, Zhipeng; Firdaus, Yuliar; Liu, Shengjian; Mcculloch, Iain; Toney, Michael F.; Beaujuge, Pierre M (Advanced Energy Materials, 2018)
Reaching device efficiencies that can rival those of polymer-fullerene Bulk Heterojunction (BHJ) solar cells (>10%) remains challenging with the ''All-Small-Molecule'' (All-SM) approach, in part because of (i) the morphological limitations that prevail in the absence of polymer and (ii) the difficulty to raise and balance out carrier mobilities across the active layer. In this report, the authors show that blends of the SM donor DR3TBDTT (DR3) and the nonfullerene SM acceptor O-IDTBR are conducive to ''All-SM'' BHJ solar cells with high open-circuit voltages (V-OC) >1.1 V and PCEs as high as 6.4% (avg. 6.1%) when the active layers are subjected to a post-processing solvent vapor-annealing (SVA) step with dimethyl disulfide (DMDS). Combining electron energy loss spectroscopy (EELS) analyses and systematic carrier recombination examinations, the authors show that SVA treatments with DMDS play a determining role in improving charge transport and reducing non-geminate recombination for the DR3:O-IDTBR system. Correlating the experimental results and device simulations, it is found that substantially higher BHJ solar cell efficiencies of >12% can be achieved if the IQE and carrier mobilities of the active layer are increased to >85% and >10(-4) cm(2) V-1 s(-1), respectively, while suppressing the recombination rate constant k to <10(-12) cm(3) s(-1).
Keywords: carrier recombination; charge transport; nonfullerene acceptors; small molecule solar cells; solvent vapor annealing

Case Study on the Dependency of the Degradation Rate on Degradation Modes and Methodology Using Monitoring Data - Denz, Janine; Peters, Marius I.; Hauch, Jens; Buerhop-Lutz, Claudia (AIP Conference Proceedings, 2022)
We present here a degradation study of a PV power plant consisting of several module pairs connecting each to a micro-inverter with monitoring. The modules comprise cell cracks, cell breakages and edge shunting. The impact of using different methodologies on the resulting relative yield loss rates is analyzed. It is demonstrated how these methods can be altered to circumvent missing irradiation sensor data generating a substitute for a relative degradation rate. The relative degradation rate of cell cracks is close to the reference with all methods and near to the detection limit which indicates little degradation for cell cracks beyond the material-inherent degradation. The modules with cell breakages and edge shunting show a higher relative yield loss of 1-3 %/a depending on the method of analysis. This indicates quite a variation is possible depending on the method thus warranting caution when evaluating degradation rates or their substitutes. It was shown that cell breakages perform increasingly worse in summer leading to even higher but seasonal performance losses. Because of that, the relative yield loss can be much higher than just the relative loss in rated power due to probably averse temperature effects on defect performance. To better assess cell crack degradation, either longer observation periods or more precise methods are needed.
CRIS-Team Scopus Importer:2022-09-16

Cathodoluminescence characterization of organic semiconductor materials for light emitting device applications - Wellmann, Peter; Karl, Ulrich; Kleber, Sebastian; Schmitt, Holger (Journal of Applied Physics, 2007)
We report the development of a cathodoluminescence-based characterization technique for the investigation of organic semiconductor materials for organic light emitting device (OLED) applications. While photoluminescence is known to predominantly address singlet exciton excitation and recombination processes, cathodoluminescence is able to simultaneously probe singlet and triplet exciton dynamics which is of importance for electroluminescence. Especially, in the case of the so-called triplet harvester materials, the generation of triplet excitons during cathodoluminescence opens the way for materials characterization without device fabrication. The paper (i) shows how cathodoluminescence can be applied for the characterization of organic semiconductor materials, (ii) points out the general measurement factors, (iii) discusses the special features of cathodoluminescence, electroluminescence as well as photoluminescence spectra, and (iv) outlines the potential of cathodoluminescence by presenting a brief study of a triplet harvester material systems. Main emphasis is put on the presentation of the characterization tool to partly replace the necessity of OLED fabrication. For that reason widely used conjugated polymers and small molecule semiconductor systems have been selected. (c) 2007 American Institute of Physics.
Keywords: cathodoluminescence; OLEDs

Cellular interfaces with hydrogen-bonded organic semiconductor hierarchical nanocrystals - Sytnyk, Mykhailo; Jakesova, Marie; Litvinukova, Monika; Mashkov, Oleksandr; Kriegner, Dominik; Stangl, Julian; Nebesarova, Jana; Fecher, Frank W.; Schoefberger, Wolfgang; Sariciftci, Niyazi Serdar; Schindl, Rainer; Heiß, Wolfgang; et al. (Nature Communications, 2017)
Successful formation of electronic interfaces between living cells and semiconductors hinges on being able to obtain an extremely close and high surface-area contact, which preserves both cell viability and semiconductor performance. To accomplish this, we introduce organic semiconductor assemblies consisting of a hierarchical arrangement of nanocrystals. These are synthesised via a colloidal chemical route that transforms the nontoxic commercial pigment quinacridone into various biomimetic three-dimensional arrangements of nanocrystals. Through a tuning of parameters such as precursor concentration, ligands and additives, we obtain complex size and shape control at room temperature. We elaborate hedgehog-shaped crystals comprising nanoscale needles or daggers that form intimate interfaces with the cell membrane, minimising the cleft with single cells without apparent detriment to viability. Excitation of such interfaces with light leads to effective cellular photostimulation. We find reversible light-induced conductance changes in ion-selective or temperature-gated channels.

Ceramic liner technology for ammonoacidic synthesis - Hertweck, Benjamin; Schimmel, Saskia; Steigerwald, Thomas; Alt, Nicolas; Wellmann, Peter; Schlücker, Eberhard (Journal of Supercritical Fluids, 2015)
The ammonoacidic crystal growth is a comprehensive method for the synthesis of novel compounds like nitrides or amindes but also for the growth of bulk single crystals like gallium or aluminum nitride for power electronics and photonics. In this report we describe a novel liner technology for growth autoclaves, showing high potential for several research purposes. Thereby the applicability of several ceramic materials as liner materials was investigated for the first time. Moreover, the effectivity of the new apparatus was verified in experimental studies. The described concept based on a silicon nitride crucible is characterized by low costs and diverse possible applications. For example its use is of advantage in fundamental research to explore new nitride materials. Furthermore, it shows high potential for X-ray imaging to investigate basic principles in growth of gallium nitride.
Keywords: Ammonothermal crystal growth; Liner technology; Ceramic materials; Corrosion; Supercritical ammonia; in situ X-ray imaging

Challenges and opportunities in upscaling inkjet-printing of OPV - Steinberger, Marc; Qingguang, Xie; Ronsin, Olivier J.J.; Maisch, Philipp; Tam, Kai Cheong; Distler, Andreas; Harting, Jens; Brabec, Christoph; Egelhaaf, Hans-Joachim (Flexible and Printed Electronics, 2024)
The power conversion efficiency and long-term stability of organic solar cells have increased tremendously over the past years, reaching up to 19.2% on research cells and 14.5% on large modules. To take the final step towards industrialization, fabrication methods that can be upscaled and directly implemented in industrial processes need to be developed. In recent years, well-known industrial techniques, like drop-on-demand inkjet printing, have been further developed within the organic photovoltaics (OPV) community, as it enables versatile printing of arbitrary, free-form organic solar modules with different colors-a key feature for modern building-integrated photovoltaics and several niche applications of OPV printed on any kind object. In this review, aside a brief summary of recent developments, we provide an overview of the biggest challenges in OPV inkjet-printing and define design rules to overcome these issues. Further perspectives of OPV inkjet-printing conclude the review.
CRIS-Team Scopus Importer:2025-02-04
Keywords: inkjet-printing; organic photovoltaics; upscaling

Characterization of Aerosol Deposited Cesium Lead Tribromide Perovskite Films on Interdigited ITO Electrodes - These, Albert; Khansur, Neamul Hayet; Almora, Osbel; Luer, Larry; Matt, Gebhard; Eckstein, Udo; Barabash, Anastasia; Osvet, Andres; Webber, Kyle Grant; Brabec, Christoph (Advanced Electronic Materials, 2021)
Aerosol deposition (AD) is a promising additive manufacturing method to fabricate low-cost, scalable films at room temperature, but has not been considered for semiconductor processing, so far. The successful preparation of cesium lead tribromide (CsPbBr3) perovskite films on interdigitated indium tin oxide (ITO) electrodes by means of AD is reported here. The 20–35 µm thick layers are dense and have good adhesion to the substrate. The orthorhombic Pnma crystal structure of the precursor powder was retained during the deposition process with no signs of defect formation. The formation of electronic defects by photoluminescence spectroscopy is investigated and found slightly increased carrier recombination from defect sites for AD films compared to the powder. A nonuniform defect distribution across the layer, presumably induced by the impact of the semiconducting grains on the hard substrate surface, is revealed. The opto-electronic properties of AD processed semiconducting films is further tested by electrical measurements and confirmed good semiconducting properties and high responsivity for the films. These results demonstrate that AD processing of metal halide perovskites is possible for opto-electronic device manufacturing on 3D surfaces. It is believed that this work paves the way for the fabrication of previously unimaginable opto-electronic devices by additive manufacturing.
CRIS-Team Scopus Importer:2021-01-22
Keywords: aerosol deposition; hysteresis; impedance spectroscopy; inorganic perovskites; photoluminescence spectroscopy

Characterization of kesterite thin films fabricated by rapid thermal processing of stacked elemental layers using spatially resolved cathodoluminescence - Künecke, Ulrike; Hetzner, Christina; Möckel, Stefan; Yoo, Hye Sun; Hock, Rainer; Wellmann, Peter (Thin Solid Films, 2015)
We report on the microstructure analysis of kesterite (Cu2ZnSnSe4) layers from rapid thermal processing of sequential elemental layers by spatially resolved cathodoluminescence in a scanning electron microscope. Energy dispersive X-ray fluorescence, X-ray diffraction and Raman spectroscopy were carried out for the validation of the findings. Special emphasis is put on the discussion of the occurrence of the secondary phases Cu2SnSe3, Cu2Se, ZnSe and SnSe. (C) 2014 Elsevier B.V. All rights reserved.
Keywords: Cu2ZnSnSe4; Cathodoluminescence; Secondary phases; Microstructure

Characterization of protrusions and stacking faults in 3C-SiC grown by sublimation epitaxy using 3C-SiC-on-Si seeding layers - Schöler, Michael; Schuh, Philipp; Litrico, G.; La Via, F.; Mauceri, M.; Wellmann, Peter (Advanced Materials Proceedings, 2017)
In this article, sublimation growth of 3C-SiC on 3C-SiC-on-Si seeding layers was evaluated by characterizing the densities of protrusions and stacking faults (SF). Both defects are among the most critical concerning the growth process and the realization of high quality material for device applications. By variation of growth parameters like temperature, growth rate and 3C-SiC-thickness we conducted a series of experiments and characterized these layers by optical microscopy and KOH etching. The protrusion density is predetermined by the seeding layers and was kept at a constant level, whereas a decrease of SF-density was observed with increasing layer thickness during subsequent sublimation growth steps. Therefore, in the case of Sublimation Epitaxy (SE) it has been found appropriate to distinguish between defects that can be reduced during SE and defects that are merely reproduced from the seeding material during sublimation growth. Furthermore, a weak trend towards a decrease of SF-density with increasing growth temperature was observed. The findings in this work demonstrates the potential of SE in growing thick and high-quality 3C-SiC layers if sufficiently good seeding layers were available.
Keywords: 3C-SiC; sublimation epitaxy; single crystalline; protrusions; stacking faults

Characterization of the phosphor (Sr,Ca)SiAlN3: Eu2+ for temperature sensing - Hertle, Ellen Elisabeth; Bollmann, Jonas; Aßmann, Simon; Kalancha, Violetta; Osvet, Andres; Batentschuk, Miroslaw; Will, Stefan; Zigan, Lars (Journal of Luminescence, 2020)
Laser-induced phosphorescence based on luminescent particles is a suitable technique for remote temperature sensing. The luminescence characteristics of the phosphor (Sr,Ca)SiAlN3:Eu2+ (”SCASN”) were investigated regarding the suitability of the material for phosphor thermometry. The phosphor has a high quantum efficiency, a very broad excitation band, an emission peak centered at about 620 nm and a short lifetime of less than 1μs, which makes it promising for thermometry measurements. After excitation at 532 nm, the luminescence emission reveals a blue shift with increasing temperature, which can be used for temperature calibration based on the two-color intensity ratio method. The excitation and emission characteristics are favorable for measurements in environments containing fuels and oils, which tend to fluorescence after UV-excitation. The phosphor allows for measurements up to 800 K, with a quenching temperature of 530 K. Spectral characteristics are presented for both bulk powder and a surface coating. For the former, a significant shift in the position of the emission peak is observed, which is most probably due to distinct re-absorption. A change in excitation laser fluence slightly affected the luminescence emission spectrum of both bulk material and coating and thus requires consideration in temperature determination.
CRIS-Team Scopus Importer:2020-06-30
Keywords: Optical sensor; Phosphor thermometry; SCASN

Characterization of ZnO Interlayers for Organic Solar Cells: Correlation of Electrochemical Properties with Thin-Film Morphology and Device Performance - Ou, Kai-Lin; Ehamparam, Ramanan; Macdonald, Gordon; Stubhan, Tobias; Wu, Xin; Shallcross, R. Clayton; Richards, Robin; Brabec, Christoph; Saavedra, S. Scott; Armstrong, Neal R. (ACS Applied Materials and Interfaces, 2016)
This report focuses on the evaluation of the electrochemical properties of both solution-deposited sol-gel (sg-ZnO) and sputtered (sp-ZnO) zinc oxide thin films, intended for use as electron-collecting interlayers in organic solar cells (OPVs). In the electrochemical studies (voltammetric and impedance studies), we used indium-tin oxide (ITO) over coated with either sg-ZnO or sp-ZnO interlayers, in contact with either plain electrolyte solutions, or solutions with probe redox couples. The electroactive area of exposed ITO under the ZnO interlayer was estimated by characterizing the electrochemical response of just the oxide interlayer and the charge transfer resistance from solutions with the probe redox couples. Compared to bare ITO, the effective electroactive area of ITO under sg-ZnO films was ca. 70%, 10%, and 0.3% for 40, 80, and 120 nm sg-ZnO films. More compact sp-ZnO films required only 30 nm thicknesses to achieve an effective electroactive ITO area of ca. 0.02%. We also examined the electrochemical responses of these same ITO/ZnO heterojunctions overcoated with device thickness pure poly(3-hexylthiophehe) (P3HT), and donor/acceptor blended active layers (P3HT:PCBM). Voltammetric oxidation/reduction of pure P3HT thin films on ZnO/ITO contacts showed that pinhole pathways exist in ZnO films that permit dark oxidation (ITO hole injection into P3HT). In P3HT:PCBM active layers, however, the electrochemical activity for P3HT oxidation is greatly attenuated, suggesting PCBM enrichment near the ZnO interface, effectively blocking P3HT interaction with the ITO contact. The shunt resistance, obtained from dark current-voltage behavior in full P3HT/PCBM OPVs, was dependent on both (i) the porosity of the sg-ZnO or sp-ZnO films (as revealed by probe molecule electrochemistry) and (ii) the apparent enrichment of PCBM at ZnO/P3HT:PCBM interfaces, both effects conveniently revealed by electrochemical characterization. We anticipate that these approaches will be applicable to a wider array of solution-processed interlayers for "printable" solar cells.
Keywords: charge selective interlayers; impedance spectroscopy; organic solar cells; phase separation; voltammetry; zinc oxide

Charge carrier dynamics in a ternary bulk heterojunction system consisting of P3HT, fullerene, and a low bandgap polymer - Koppe, Markus; Egelhaaf, Hans-Joachim; Clodic, Ewan; Morana, Mauro; Lueer, Larry; Troeger, Anna; Sgobba, Vito; Guldi, Dirk Michael; Ameri, Tayebeh; Brabec, Christoph (Advanced Energy Materials, 2013)
The photoresponse of P3HT:PC BM based organic solar cells can be enhanced by blending the bulk heterojunction with the low band gap polymer Si-PCPDTBT. Organic solar cells containing the resulting ternary blend as the photoactive layer deliver short circuit currents of up to 15.5 mA cm. Morphological studies show modest phase separation without the perturbation of the crystallinity of the P3HT:PC BM matrix, in accordance with the measured acceptable fill factors. Picosecond time-resolved pump-probe spectroscopy reveals that the sensitization of P3HT:PC BM with Si-PCPDTBT involves the transfer of photogenerated positive polarons from the low band gap polymer to P3HT within few hundreds of picoseconds. Intensity dependent experiments in combination with global fitting show that the charge transfer from Si-PCPDTBT to P3HT competes with non-geminate charge carrier recombination of the holes in the Si-PCPDTBT phase with electrons in the PC BM phase, both processes being of diffusive nature. At excitation densities corresponding to steady state conditions under one sun, modelling predicts hole transfer efficiencies exceeding 90%, in accordance with IQE measurements. At higher pump intensities, bimolecular recombination suppresses the hole transfer process effectively. © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Charge Carrier Extraction in Organic Solar Cells Governed by Steady-State Mobilities - Le Corre, Vincent Marc; Rahimi Chatri, Azadeh; Doumon, Nutifafa Y.; Koster, L Jan Anton (Advanced Energy Materials, 2017)
Charge transport in organic photovoltaic (OPV) devices is often characterized by steady-state mobilities. However, the suitability of steady-state mobilities to describe charge transport has recently been called into question, and it has been argued that dispersion plays a significant role. In this paper, the importance of the dispersion of charge carrier motion on the performance of organic photovoltaic devices is investigated. An experiment to measure the charge extraction time under realistic operating conditions is set up. This experiment is applied to different blends and shows that extraction time is directly related to the geometrical average of the steady-state mobilities. This demonstrates that under realistic operating conditions the steady-state mobilities govern the charge extraction of OPV and gives a valuable insight in device performance.
Keywords: bulk-heterojunction solar cells; charge carrier extraction; organic photovoltaics; steady-state mobility

Charge transport and recombination in low-bandgap bulk heterojunction solar cell using bis-adduct fullerene - Azimi, Hamed; Senes, Alessia; Scharber, Markus C.; Hingerl, Kurt; Brabec, Christoph (Advanced Energy Materials, 2011)
Charge transport and recombination are studied for organic solar cells fabricated using blends of polymer poly[(4,4′-bis(2-ethylhexyl)dithieno[3, 2-b:2′,3′ -d]silole)-2,6-diyl-alt-(4,7-bis(2-thienyl)-2,1,3- benzothiadiazole)-5,5′-diyl] (Si-PCPDTBT) with [6,6]-phenyl-C -butyric acid methyl ester (mono-PCBM) and the bis-adduct analogue of mono-PCBM (bis-PCBM). The photocurrent of Si-PCPDTBT:bis-PCBM devices shows a strong square root dependence on the effective applied voltage. From the relationship between the photocurrent and the light intensity, we found that the square-root dependence of the photocurrent is governed by the mobility-lifetime ( ) product of charge carriers while space-charge field effects are insignificant. The fill factor (FF) and short circuit current density ( J ) of bis-PCBM solar cells show a considerable increase with temperature as compared to mono-PCBM solar cells. SCLC analysis of single carrier devices proofs that the mobility of both electrons and holes is significantly lowered when replacing mono-PCBM with bis-PCBM. The increased recombination in Si-PCPDTBT:bis-PCBM solar cells is therefore attributed to the low carrier mobilities, as the transient photovoltage measurements show that the carrier lifetime of devices are not significantly altered by using bis-PCBM instead of mono-PCBM. © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
Keywords: Applied voltages; Benzothiadiazoles; Bis-adducts; Bulk heterojunction solar cells; Charge transport and recombination; Electrons and holes; Fill factor; Light intensity; Methyl esters; Organic solar cell; Single carrier; Space charge field; Square-root dependence; Transient photovoltage measurements Engineering controlled terms: Heterojunctions; Photocurrents; Polymer blends; Silicon Engineering main heading: Solar cells

Charge transport in nanoparticular thin films of zinc oxide and aluminum-doped zinc oxide - Lenz, Thomas; Richter, Moses; Matt, Gebhard; Luechinger, N.A.; Halim, S.C.; Heiß, Wolfgang; Brabec, Christoph (Journal of Materials Chemistry C, 2015)
In this work, we report on the electrical characterization of nanoparticular thin films of zinc oxide (ZnO) and aluminum-doped ZnO (AZO). Temperature-dependent current-voltage measurements revealed that charge transport for both, ZnO and AZO, is well described by the Poole-Frenkel model and excellent agreement between the experimental data and the theoretical predictions is demonstrated. For the first time it is shown that the nature of the charge-transport is not affected by the doping of the nanoparticles and it is proposed that the Poole-Frenkel effect is an intrinsic and universally limiting mechanism for the charge transport in nanoparticular thin films with defect states within the bandgap. © The Royal Society of Chemistry 2015.
Keywords: Engineering controlled terms: Aluminum; Carrier transport; Optical films; Semiconductor doping; Thin films; Zinc; Zinc oxide Aluminum-doped zinc oxide; Aluminum-doped ZnO; Current voltage measurement; Electrical characterization; Poole-Frenkel effect; Poole-Frenkel model; Temperature dependent; Zinc oxide (ZnO) Engineering main heading: Oxide films

Charge Transport Layers Limiting the Efficiency of Perovskite Solar Cells: How To Optimize Conductivity, Doping, and Thickness - Le Corre, Vincent Marc; Stolterfoht, Martin; Perdigón-Toro, Lorena; Feuerstein, Markus; Wolff, Christian M; Gil-Escrig, Lidón; Bolink, Henk J; Neher, Dieter; Koster, L Jan Anton (ACS Applied Energy Materials, 2019)
Perovskite solar cells (PSCs) are one of the main research topics of the photovoltaic community; with efficiencies now reaching up to 24%, PSCs are on the way to catching up with classical inorganic solar cells. However, PSCs have not yet reached their full potential. In fact, their efficiency is still limited by nonradiative recombination, mainly via trap-states and by losses due to the poor transport properties of the commonly used transport layers (TLs). Indeed, state-of-the-art TLs (especially if organic) suffer from rather low mobilities, typically within 10(-5) and 10(-2) cm(-2) V-1 s(-1), when compared to the high mobilities, 1-10 cm(-2) V-1 s(-1), measured for perovskites. This work presents a comprehensive analysis of the effect of the mobility, thickness, and doping density of the transport layers based on combined experimental and modeling results of two sets of devices made of a solution-processed high-performing triple-cation (PCE approximate to 20%). The results are also cross-checked on vacuum-processed MAPbI(3) devices. From this analysis, general guidelines on how to optimize a TL are introduced and especially a new and simple formula to easily calculate the amount of doping necessary to counterbalance the low mobility of the TLs.
Keywords: perovskite solar cells; transport layers; conductivity; doping; charge transport

Chemical stability of carbon-based inorganic construction materials for in situ x-ray measurements of ammonothermal crystal growth of nitrides - Schimmel, Saskia; Meisel, Magnus; Hertweck, Benjamin; Steigerwald, Thomas; Nebel, Christoph; Alt, Nicolas; Schlücker, Eberhard; Wellmann, Peter (5th German-Swiss Conference on Crystal Growth, 2017)

Chemical stability of carbon-based inorganic materials for in situ x-ray investigations of ammonothermal crystal growth of nitrides - Schimmel, Saskia; Künecke, Ulrike; Meisel, Magnus; Hertweck, Benjamin; Steigerwald, Thomas; Nebel, Christoph; Alt, Nicolas; Schlücker, Eberhard; Wellmann, Peter (Journal of Crystal Growth, 2016)
The chemical stability of diamond, silicon carbide, vitreous carbon, and boron carbide in supercritical ammonia containing different mineralizers was investigated. The materials were found to show good corrosion resistance in the presence of selective or all tested mineralizers.Diamond was found to be virtually inert in both ammonoacidic and ammonobasic reaction media.Silicon carbide showed good chemical stability in varying ammonothermal reaction media.The chemical stability of vitreous carbon was found to depend on its manufacturing temperature.Corrosion of boron carbide strongly depends on the mineralizer used as well as on applied mechanical stress.Based on their chemical stability and mechanical properties, the applicability of the materials in the respective ammonothermal reaction media as construction materials is evaluated. Additionally, the applicability of the materials as a window material for both high energy . in situ x-ray imaging and low energy . in situ x-ray diffraction is discussed.
Keywords: A1. Solubility; A1. Solvents; A1. X-ray diffraction; A2. Ammonothermal crystal growth; B1. Inorganic compounds; B1. Nitrides

Chemical Vapor Deposition of 3C-SiC on [100] Oriented Silicon at low Temperature < 1200°C for Photonic Applications - Kollmuß, Manuel; Köhler, Johannes; Ou, H.; Fan, W.; Chaussende, D.; Hock, Rainer; Wellmann, Peter (Materials Science Forum, 2022)
3C-SiC films have been grown on [100] n-doped Si substrates in a horizontal cold wall CVD reactor. Without the use of plasma enhancement, the precursors silane and propane are used to deposit silicon carbide films at T < 1200°C. The structure of the grown films has been investigated via FESEM, XRD and Raman spectroscopy. It has been found that the growth rates are between 200 and 300 nm/h. Additionally, structural analysis give evidence of polycrystalline phases. Reasons for that could be insufficient cracking of the precursors and homogenous nucleation of Si species in the gas phase.
CRIS-Team Scopus Importer:2022-12-16
Keywords: 3C-SiC; cold wall reactor; CVD; heteroepitaxy; low temperature; void